Notes on New Zealand Recent and Tertiary Mussels (Mytilidae)
[Received by the Editor, December 8, 1958.]
The genus Botula Mörch is introduced into the New Zealand fauna for Botula molina n.sp. (Castlecliffian, Lower Pleistocene), attributed to a new subgenus Notobotula. The new genus Ryenella (Lanistina Soot-Ryen, non J. E. Gray) is proposed, with Musculus impactus (Hermann) as type.
The following innovations are introduced in the classification of New Zealand Mytilidae: Mytilus aoteanus Powell is ranked as a subspecies of M. edulis Linnaeus, M. canaliculus and M. tetleyi are classed in the genus Perna Retzius (= Chloromya auct.), M. torquatus Marshall in Septifer Recluz, Zelithophaga (?) nelsoniana (Suter) is returned to Lipthophaga, Trichomusculus barbatus (Reeve) and T. lornensis Laws are classed in Gregariella Monterosato, Dacrydium pelseneeri Hedley in Quendreda Iredale, as a subgenus, and D. radians Suter in the genus Crenella Brown. Modiolus huttoni Suter is illustrated and recorded from Lower Pleistocene (Nukumaruan-Castlecliffian) sediments in North and South Islands.
In the course of work on a checklist of New Zealand Tertiary Mollusca, several changes were made in the generic classification of New Zealand Mytilidae, fossil and living. Some of the changes result from the application to New Zealand forms of the results of Soot-Ryen's review (1955) of the West American Mytilidae. Others are due to study of types and other specimens in the New Zealand Geological Survey. The opportunity is also taken to review the stratigraphic occurrence of Mytilid genera in the New Zealand Cenozoic.
Genus Mytilus. Linnaeus, 1758
Mytilus edulis aoteanus Powell (Fig. 1 in text).
1958. Mytilus aoteanus Powell, Rec. Auck. Inst. Mus. 5 (1–2): 87, pl. 12, f. 5, Text-fig. A.
As recorded by Powell (1955: 23) the writer had separated New Zealand specimens from Australian shells classed as planulatus Lamarck. Powell distinguished the New Zealand population by the longer dorsal slope and fewer hinge teeth. In addition, East Australian shells differ from New Zealand ones in the shape of the posterior retractor scar. New Zealand shells have a narrow retractor scar separated from the posterior adductor scar by a rather deep re-entrant angle (Fig. 1). Australian shells have a wider retractor, rather irregularly bounded on the inside, passing into the adductor with only a shallow separating re-entrant (Fig. 3). The anterior adductor scar is relatively larger in most New Zealand shells, which thus approach the condition in the Boreal form M. e. edulis Linnaeus (Fig. 2).
The close similarity in shell form, in habitat, and in circumpolar zonal distribution in cool temperate seas, between the southern populations of Mytilus s. str. and the Boreal edulis are best reflected in their classification by use of trinomial nomenclature, as advocated by Soot-Ryen (1955: 29) and some earlier writers.
Fig. 1.—Mytilus edulis aoteanus Powell. Campbell Island.
Fig. 2.—Mytilus edulis edulis Linnaeus. Staten Island, New York.
Fig. 3.—Mytilus edulis planulatus Lamarck. Tasmania.
Soot-Ryen comments that Mytilus s. str. seems to be of relatively recent origin, as no records of species which certainly belong to the restricted genus are older than Pliocene, and he suggests that M. edulis has had at least partly the same history as Aulacomya in, geologically speaking, relatively recent times. The known fossil occurrences of M. e. aoteanus (Hawera Series only) suggest that the group is a late-comer to New Zealand, but the true position may be obscured by the rarity of the rocky-shore facies in Tertiary deposits.
In view of its present restricted distribution on the coasts of Auckland, the occurrence of fossil M. e. aoteanus in a shellbed exposed by trenching at Devonport, Auckland (GS 6220; ? Flandrian) is worth recording.
Genus Perna. Retzius
1788. Dissertatio historica-naturalis nova Testaceorum genera, p. 20.
Type. (by subsequent designation, Soot-Ryen, 1955): Perna magellanica Retzius = Mya perna Linnaeus.
Soot-Ryen (1955: 29) has shown that Perna Retzius (non Bruguière, 1792, nec Adams, 1858) is the oldest name for the group of mussels generally classed as Chloromya Mörch, 1853.
Perna canaliculus (Gmelin, 1791)
1791. Mytilus canaliculus Gmelin (ex Martyn), Systema Naturae, ed. 13, I: 3363.
In Opinion 456, the International Commission on Zoological Nomenclature (1957 A) ruled that Martyn's Universal Conchologist (1784) possesses no status in zoological nomenclature. In Opinion 479 (1957B), the Commission placed the name Mytilus canaliculus Gmelin on the Official List of Specific Names in Zoology, with the specimen figured by Martyn as holotype.
Suter placed this species under Chloromya as a subgenus, and its classification as Perna follows from Soot-Ryen's work (1955). Fossil records of canaliculus extend its geological range back to Opoitian (Kaawa Creek, Laws, 1936), but fossil specimens are seldom well enough preserved for critical study.
The specific name is a noun (canaliculus = a small channel) in apposition to the generic name, and thus not inflected.
Perna tetleyi (Powell & Bartrum, 1929)
1929. Mytilus tetleyi Powell & Bartrum, Trans. N. Z. Inst. 60 399, pl. 40, fig. 46, 47, 103.
Powell & Bartrum compared M. tetleyi (Waiheke Island, Altonian) with the living canaliculus and it may be provisionally classed in Perna, although its resilial characters and muscle scars are unknown.
Aulacomya maoriana (Iredale, 1915)
Aulacomya is a zonal Subantarctic genus, so that the first appearance of A. maoriana in the Waitotaran of Otahuhu and Reefton district is in keeping with the hypothesis of late Tertiary cooling. The only other Tertiary record of the genus is Aulacomya willetsi (Marwick) from the Chatham Island deposits that are probably Lower Oligocene, but the specimens are not well enough preserved, particularly their interiors, for the relationship to be quite certain.
Genus Brachidontes Swainson 1840
1840. A Treatise on Malacology: 384.
Type (by monotypy): Modiola sulcata Lamarck 1819 (non 1805) = Mytilus citrinus Roding, 1798 = Arca modiolus Linnaeus, 1767 (fide Soot-Ryen, 1955).
This generic name has been retained by Cotton & Godfrey (1938), Macpherson & Chapple (1951) and Kershaw (1955), following Hedley (1918) and May (1921), for the three Australian ribbed mussels, Mytilus erosus Linnaeus, M. rostratus Dunker, and M. hirsutus Lamarck. Of the three, M. erosus is most like the type species of Brachidontes in its shape, in its short ligament and its tooth-like crenulations along the dorsal margin behind the ligament, but differs in its raised and calloused anterior adductor, terminal umbone, and few poorly developed hinge teeth. Nevertheless, the affinity is close enough to support its retention in Brachidontes, a course adopted by Allan (1950) and Laseron (1956).
A second Australian “Brachidontes”, Mytilus rostratus (Dunker) has been separated as type of a genus Austromytilus Laseron (1956) with ample justification. Laseron described the distinctive anterior adductor muscle scar of Austromytilus as “small, round, and deeply excavated”, but it is, on the contrary, of average size, generally somewhat elongated, and raised into a peculiar boss (Iredale, 1924: 196), best developed in adult shells. Laseron included the type alone, but a congeneric species is M. linguatulus Tate from the Kalimnan (Pliocene) of Muddy Creek.
The third Australian species, Mytilus hirsutus Lamarck, differs from Brachidontes in shape, with a relatively longer ligament occupying most of the dorsal margin, twisted beak, and in its fine regular sculpture which increases as much by interpolation as by bifurcation, and in the possession of a dense periostracum of fine barbed hairs, so that, as Iredale (1924) advocated, it deserves generic separation under Trichomya.
Trichomya has a Pliocene species in Victoria (Mytilus hamiltonensis Tate) and was present in New Zealand during the Middle Tertiary, but Brachidontes and Austromytilus have not been recognised on this side of the Tasman.
Genus Trichomya Ihering
1900. Proc. Malac. Soc. Lond. 4: 87.
Type (by original designation): Mytilus hirsutus Lamarck.
Trichomya huttoni (Cossmann)
1885. Mytilus striatus Hutton, Trans N.Z. Inst. 17: 332.
1915. Mytilus (Aulacomya) striatus Hutton; Suter, N.Z. geol. Surv. Pal. Bull. 3: 50,. pl. 4, fig. 21.
1916. Mytilus huttoni Cossmann. Rev. Crit. Pal., 20: 11 (n.nov. for M. striatus Hutton non Montague, 1803, etc.).
1917. Mytilus (Aulacomya) huttoni Cossmann; Suter, N.Z. geol. Surv. Pal. Bull. 5: 84.
1927. Trichomya huttoni (Cossmann); Finlay, Trans. N.Z. Inst. 57: 450.
T. huttoni is closely similar to the type species of Trichomya and its Pliocene forerunner T. hamiltonensis Tate, but differs in its narrower shell, which is less alate dorsally, and in the more convex ventral margin behind the beak.
The type is from the upper shell bed of Broken River, long classed in the Pareora Series, but of uncertain age, probably Southland Series, perhaps Altonian. Other
specimens are known from Target Gully, Oamaru, both from the underlying greensand which Park classed in the Hutchinsonian (Park, 1920: 8) and from the main shell bed (Awamoan).
An older New Zealand record of Trichomya is from GS 4676, Harper River, Canterbury, Waitakian Stage, with Athlopecten (Suggate & Wilson, 1958: 41). The specimens are larger than huttoni and differ in shape, being more alate, like the Australian species, so they may represent a new species, but they are not well preserved.
Genus Septifer Recluz
1848. Revue Zool.: 275.
Type (subsequent designation, Stoliczka, 1871): Mytilus bilocularis Linnaeus.
Septifer torquatus (Marshall) (Plate 13, Fig. 14, 15; Fig. 4 in text)
1918. Mytilus torquatus Marshall, Trans. N.Z. Inst. 50: 271, p. 21, fig. 3, 3a.
1927. Trichomya torquata (Marshall); Finlay, Trans. N.Z. Inst. 57: 450.
Although Finlay wrote that M. torquatus is the ancestor of M. huttoni, the two species differ in shape and sculpture sufficiently to arouse suspicion of generic difference. Excavation of the hinge area of Marshall's holotype (his fig. 3) and paratype has revealed a well-developed septum (Fig. 4), characteristic of Septifer, and the sculpture and high arched form agree with this genus. This reclassification of a Pakaurangi Point (Altonian) species in a warm-water genus is quite in keeping with the known subtropical relationships of the Altonian, particularly in Northland.
S. torquata is quite closely related to the contemporary Australian S. fenestratus (Tate), having a well developed dorsal wing above a concave posterior margin and a pouting anteroventral outline (as in many Modiolus). Both these Lower Miocene forms differ in their narrowly inflated form from the widely-distributed Indo-Pacific S. bilocularis and from the living New South Wales species, S. australis Laseron, they are perhaps more closely related to S. excisus Wiegmann, another living Indo-Pacific species The occurrence of a Miocene Septifer in New Zealand therefore throws no light on the Recent record of a stray S. bilocularis in the Bay of Plenty (Powell, 1954); two separate immigrations of Septifer are indicated by the scanty records one Miocene, the other Holocene.
Genus Modiolus Lamarck
Volsella Scopoli, 1777, has been suppressed by the International Commission on Zoological Nomenclature (1955) and Modiolus Lamarck, 1799, established as a nomen conservandum.
Modiolus aerolatus (Gould).
Modiolus altijugatus Marwick.
The living species M. aerolatus (Gould) is recorded as early as the Opoitian from Taranaki (Omono S.D., GS 7231) and is preceded by M. altijugatus Marwick in the Kapitean and Tongaporutuan of several districts M. altijugatus occurs in the Shoal Point Formation (about Opoitian) of Campbell Island (Fleming, 1950) and has recently been identified in the Opoitian of Wairoa district (Hawke's Bay). More data are needed to clarify the relationships of these apparently successive forms in the Opoitian Stage.
The other living species of Modiolus have no fossil record. M. neozelanicus (Iredale) lives on rocky shores, an environment seldom represented in the Tertiary. Estuarine lagoons, such as M. fluviatilis (Hutton) inhabits, are, however, occasionally represented by sediments, particularly in the Wanganui Series, so its absence as a fossil may indicate that it is a late arrival in New Zealand. In the early Pleistocene the estuarine environment was, in fact, occupied by a giant Modiolus that has previously been poorly known (see below). Other occurrences of poorly-preserved Modiolus, as yet undescribed, extend the Tertiary range of the genus in New Zealand
back to the Waitakian (GS 4676, Harper River), but it is rare, considering that Modiolus was present in the Upper Cretaceous (M. cf. typica (Forbes)) and lives in a wide range of habitats.
Modiolus huttoni Suter (Plate 13, Figs. 8–13)
1873. Modiolus sp. ind., Hutton, Cat. Tert. Moll. Echin. N.Z.: 26.
1914. Modiolus huttoni Suter, N.Z. geol. Surv. pal. Bull. 2: 39, pl. 5, fig. 3.
Buchanan's drawing of the battered holotype (here refigured, Fig. 8) does scant justice to this species, which has proved to be not uncommon in silty and sandy beds of shallow (probably intertidal) estuarine facies, in the Wanganui Series. The type, from “Lower Gorge of the Waipara,” retains conglomerate matrix within its beak, showing that it came from the upper beds (Wanganui Series) and not from the Waiauan shell beds of the Lower Waipara Gorge. Mr. D. R. Gregg collected virtual topotypes (but in different matrix) from below Greenwoods Bridge (GS 4958, grid reference S68/142045) in beds of estuarine facies with Chione and Lutraria, which overlie Waitotaran and may be Nukumaruan, and Thomson had collected others from the Motunau Beds opposite Mount Brown Cuesta in the Middle Waipara.
In the North Island, Modiolus huttoni was recorded as Modiolus aff. fluviatilis (Hutton) and Modiplus n.sp. (Fleming, 1953: 148–166) from several formations in the Nukumaru and Maxwell groups of the Wanganui Nukumaruan (Marahauan Substage) and was misidentified as M. aerolatus in the Upper Nukumaruan of Dannevirke Subdivision (Fleming & Marwick, 1953, Table XXII; GS 2362, 2366). Poorly preserved specimens also occur in the upper formations of the Kidnapper Group, Southern Hawke's Bay (GS 5306—7) which are classed as Castlecliffian (Fleming, 1957: 58).
The known range is thus Nukumaruan, perhaps Upper Waitotaran, to Castlecliffian.
In ecology, M. huttoni resembled the Recent M. fluviatilis, but in size it is more like M. aerolatus, a species favouring open coasts of normal salinity. M. huttoni differs from all New Zealand species in its heavily built shell; its dorsal and ventral margins are more parallel than in other New Zealand forms, and there is a broader antero-ventral pout. A well-defined keel runs from beak to postero-ventral margin, concave downwards. The anterior adductor scar is well defined, generally sunken and surrounded by callus, and there are commonly pits representing siphonal retractor muscles in the central part of the valve (Fig. 11).
Despite its resemblances to M. aerolatus in size, M. huttoni seems to be more closely related to M. fluviatilis which it resembles not only in ecology, but apparently in the possession of a dark blackish periostracum (Fig. 9), and in general outline. The resemblance of M. huttoni to another giant fossil species, Modiolus brocchii Mayer, from the Vienna Miocene and Italian Pliocene (Hoernes, 1870, pl. 45, f. 13) may indicate affinity, despite the great differences in age and distribution.
Amygdalum striatum (Hutton, 1873) (Plate 13, Fig. 17)
Amygdalum dolichum (Suter, 1917)
Material and data are as yet inadequate to decide the status of these nominal species A. dolichum was described from an unknown horizon at Weka Pass, and A. striatum from “Shakespeare Cliff”, so that its precise horizon within the Wanganui Series is also uncertain. Other New Zealand records of Amygdalum are from the Fan Coral Beds, Trelissick Basin (Duntroonian); Waikawau Creek (GS 272, ? Waitakian); Kakahu (GS 577, Awamoan); Momoeatoa, Chatham Island (GS 6900, ? Kapitean); near Trig. B, Patutahi S.D., Ormond beds (Opoitian); Upper Okiwa Group, Parapara Road, Wanganui (GS 4199, Hautawan Substage, Nukumaruan); and Tahoraite S.D., Dannevirke (GS 2665, Marahauan Substage, Nukumaruan). Hutton's type of striatum is in fine pale silt. Other specimens from “Wanganui”
at the Geological Survey are free of matrix, so are probably from a sand, and were associated with Landguard Bluff specimens in a collection not precisely localized. They were listed from Landguard Bluff by Fleming (1953: 244), but this Castle-cliffian record needs confirmation.
The Wanganuian specimens of A. striatum reach a very large size (Fig. 17); the largest, from GS 2665, is 75 mm long. They differ from the living Amygdalum beddomei Iredale (Tasmania and New South Wales) in size and shape, having more divergent dorsal and ventral margins, with their beaks further forward.
Suter received specimens that he labelled Modiolus japonicus Dunker from Bollons, “said to have been found in New Zealand” but rejected the record, and there has been no later report to suggest that Amygdalum survived the Wanganuian in New Zealand.
Genus Botula Morch
1853. Catal. Conchyl. Yoldt, 2: 55.
Type (by subsequent designation, Dall, Bartsch and Rehder, 1938): Mytilus fuscus Gmelin (West Indies). Figured, Soot-Ryen, 1955, pl. 9, fig. 52, text-fig. 70; Perry & Schwengel, 1955, pl. 7, f. 42).
Iredale overlooked this type designation when he selected the same species in 1939. Botula was ranked as a subgenus of Modiolus by Dall (1898) and Ihering (1900) and considered to be intermediate between the boring Lithophaga and the nestlers, as regards externals.
“Surface deeply concentrically sulcate, shell inflated, with conspicuously spiral umbones, the epidermis polished” (Dall). “The anterior retractor is placed on the margin of the shell just below the umbones. The posterior adductor is small and the posterior retractor leaves a small scar above the adductor. There are traces of siphonal retractor muscles in the middle of the valve…. The margin above the ligament and just behind it is finely transversely striated.” (Soot-Ryen, 1955: 83–4.)
According to Abbott (1954: 356) the type species lives attached in clusters to wood and rocks.
Iredale (1939: 414) separated Botulopa n. gen. for a Queensland coral reef form B. silica infra Iredale, because it is a true borer, not a nestler, is smooth, not sulcate, with umbones not conspicuously spiral, and lacks the peculiar muscle scars of Botula.
Subgenus Notobotula Fleming n. subgen.
Type: Botula (Notobotula) molina Fleming n. sp., Lower Pleistocene, New Zealand.
The species described below agrees reasonably well in shape and general structure with the type species of Botula and with others so classified, including specimens identified as Botula subcordata (d'Orbigny) from the Burdigalian of Carrejan, Modiolus hörnesi Reuss (Vienna Basin), and the Paris Eocene species Lithodomus cordatus Lamarck and L. argentinus Deshayes, figured by Cossmann & Pissarro (1904–6, pl. 38, f. 116·3, 116·4). The New Zealand form differs from all these species in its anterior adductor scar, which is very elongated, is set close above the curve of the anterior ventral margin, and is raised on a thickened step, bordered above by a buttress-like ridge (Figs. 5, 22–4). The anterior retractor is circular, and lies within the umbonal cavity, just behind the beaks (a normal situation in Mytilids), whereas in B. fusca Gmelin, as illustrated by Soot-Ryen (1955, f. 70), it lies immediately above the margin, and is elongated along the hinge plate.
As discussed below, Notobotula is also distinguished from Botula s. str. and from Botulopa by its ecology.
Figs. 8–13.—Modiolus huttoni Suter. Fig. 8—Holotype (TM 2129). Lower Waipara Gorge. Fig. 9—Mangahou Siltstone, Ototoka (TM 2130). Figs. 10, 12, 13—Nukumaru Brown Sand, Wanganui River (TM 2132–3). Fig. 11—Takapau S.D. (TM 2131). Natural size. Figs. 14, 15—Septifer torquatus (Marshall). Holotype (TM 2122), X 1 and X 2. Pakaurangi Point. Fig. 16—Lithophaga nelsoniana Suter. Holotype (TM 2134), X 2. Port Hills, Nelson. Fig. 17—Amygdalum striatum (Hutton). Tahoraite Survey District (TM 2137), X 1.
Fig. 4.—Septifer torquatus (Marshall). Holotype, Pakaurangi Point, Kaipara; showing septum and reconstructed outline.
Fig. 5.—Botula (Notobotula) molina Fleming n. sp. Buttressed anterior adductor scar, transverse striations at dorsal margin, and anterior retractor scar in umbonal cavity.
Botula (Notobotula) molina Fleming n. sp. (Plate 14, Fig. 18–24; Fig. 5 in text) 1953. Modiolus n. sp. Fleming, N.Z. geol Surv. Bull. 52: 225.
Material: Holotype, right valve (TM 2124) and four paratypes (TM 2125–2128) in the New Zealand Geological Survey.
Description: Shell small, thin, fragile, shining; beak low, close to anterior margin. Posterior dorsal margin short, straight or gently rounded, passing smoothly into gently rounded posterior margin. Posterior ventral margin broadly rounded, passing into straight or gently concave ventral margin which is parallel with the long axis of the shell. Surface with irregular growth sulci and faint fine radial striations. Hinge-line narrow below beaks, thickened in front, and expanded and shallowly excavated behind. Ligament area narrow; postero-dorsal margin marked by faint almost vertical striae. Anterior adductor muscle scar long, narrow, following anterior margin of shell, bounded above by a strong, tapering buttress-ridge arising beneath the beaks. Posterior adductor not clearly defined. Anterior retractor scar almost circular, within the umbonal cavity, slightly behind the beak.
Dimensions: Length (oblique), 17; width, 9; inflation, 4 mm (holotype, right valve). The largest paratype is 18 mm long.
Locality: GS 4030, uppermost six feet of Pinnacle Sandstone at the Pinnacles (“Windmill Gully”), Castlecliff; not uncommon but difficult to collect.
Stratigraphic Position: Zone of Pecten jacobaeus tot Fleming, in the Pinnacle Sand, Putikian Substage, Castlecliffian Stage (Lower Pleistocene).
Ecology: One of the paratypes is the mould of a complete individual with valves closed, and the fragile valves cannot have been transported far. The specimens were found widely scattered in richly fossiliferous silty fine sand containing Coluzea, Antisolarium, Pecten, Xenophalium, etc. (see Fleming, 1953: 224), representing offshore shelf deposits probably in a depth of about 40 fathoms. The inferred habitat stands in strong contrast with that of Botula s. str. (clustering on wood and rocks) and of Botulopa (on the reef flat, boring in dead coral rock in an advanced state of decomposition).
The specific name refers to the type locality, “Windmill Gully”.
Genus Zelithophaga Finlay
1927. Trans N.Z. Inst. 27: 451.
Type (by original designation): Lithodomus truncatus Gray, Recent, New Zealand.
Zelithophaga is more closely related to Diberus Dall (type: L. plumula Hanley) than to Lithophaga, but differs in lacking the radial sulci noted by Dall for his
“section”, in having higher beaks, set further back; the dorsal margin is arched, and the posterior incrustation lacks regular sculpture.
Zelithophaga truncata (Gray)
1843. Lithodomus truncatus Gray, in Dieffenbach's “New Zealand”: 259.
The only definite fossil records of this species in N.Z. Geological Survey collections are from GS 4174, Rapanui Marine Sand (Oturian Stage) at the mouth of Wairoa Stream, Waipipi (Waverley) and from GS 6481, base of elevated Pleistocene sands, unconformable above Opoitian sandstone, at sea-level on the shore below the rest hut, Cape Kidnappers.
Zelithophaga n. sp. (?)
Seven poorly preserved specimens from limestone near the base of the Upper Kumeroa Formation of Takapau Survey District (GS 2318, Tourerere Hills) agree with Z. truncata in their characteristic shape anteriorly, but reach a larger size (dorso-ventral height 18 mm) than any Recent specimens seen, and may be distinct. They serve to extend the range of Zelithophaga back to the Lower Pleistocene.
Genus Lithophaga Röding
Type (by monotypy): L. mytuloides Röding = Mytilus lithophagus Linnaeus.
Lithophaga nelsoniana Suter (Plate 13, Fig. 16)
1917. L. nelsoniana Suter, N.Z. geol. Surv. pal. Bull. 5: 68, pl. 7, f. 13.
1927. Zelithophaga (?) nelsoniana (Suter); Finlay, Trans. N.Z. Inst. 57: 451.
Finlay wrote that this species “may possibly be congeneric” with Zelithophaga truncata, but Dr. J. Marwick has pointed out that it agrees more closely with Lithophaga in its thin, anteriorly-tapering shell. The locality, in the Port Hills, Nelson (coll. W. F. Worley), has not been re-located by later workers, but is presumably in the Landon Series.
Genus Musculus Röding
Type (by subsequent designation, Iredale, 1915: 485): Musculus discors = Mytilus discors Linnaeus.
Musculus (?) elongatus (Hutton)
1873. Crenella elongata, Hutton, Cat. Tert. Moll. Ech. N.Z.: 25.
1915. Modiolaria elongata (Hutton); Suter N.Z. geol. Surv. pal. Bull. 3: 51, pl. 1, f. 4.
Distinction of Musculus from Ryenella depends on anatomy and on the arrangement of retractor muscles, which has not been determined in this species. The small, delicate, finely-ribbed shell of elongata agrees better with Musculus than with Ryenella, however, so the species is here retained, provisionally, in Musculus (s. lat.).
No definite records are known away from the Duntroonian tuffs of the type area (Broken River; Fan Coral Bed at junction of Thomas and Porter rivers, GS 239; tuffaceous greensand, Whitewater Creek). In 1942, the writer collected poor impressions of similar small Musculus from tuffaceous sandstone on Musgrave Peninsula, Auckland Islands, associated with Divaricella and Offadesma. Further records probably of this genus are from Waitahu Bridge, Reefton (GS 2993, Kaiatan), and from Pakaurangi Point (Laws, 1944, p. 298, Altonian).
Genus Ryenella Fleming n. gen.
Type: Mytilus impactus Hermann, Naturforscher, XVII: 152. Figured: Suter, 1915. Man N.Z. Moll. (Atlas), pl. 58, f. 7, Powell, 1957, Shells of N.Z., pl. 10, f. 1.
According to Soot-Ryen (1955: 73) species with quite different anatomy have been placed in Musculus. M. impactus Hermann, and similar species, here grouped in Ryenella, are more inflated than typical Musculus and the arrangement of
retractor muscles is different, the posterior retractors having “a strong, elongated branch fastened along the dorsal margin and a single slender branch fastened above the posterior adductor”, whereas in Musculus they are continuous and united with the posterior adductor. Soot-Ryen recommended generic separation of M. impactus Hermann (with M. marmoratus (Forbes), M. cummingianus (Reeve), and M. lebourae White) from Musculus, and proposed use of the generic name Lanistina in the meantime for the impactus group.
Lanistina Gray 1847 was introduced as a nom. nov. for Lanistes Swainson 1840 (Humphrey, MS) described with a single species, Mytilus discors, with the reference Enc. Meth. 204, f. 5, which Soot-Ryen states is Musculus impactus (Hermann). But Mytilus discors Linnaeus was already well enough known to suggest that citation in the Encyclopèdie Mèthodique without author referred to Linnaeus' nominal species, and in fact this name from Encyclopèdie Mèthodique is not listed as a separate taxon by Sherbourne in the Index Animalium. Further, Hermannsen (1846: 575) cited Mytilus discors Linn. as type of Lanistes “Humphrey”. There is no evidence that Swainson intended to cite a different taxon from Mytilus discors Linnaeus under his Lanistes, and his reference to a figure of a what now appears to be a different species should not affect the issue. Swainson, in proposing Lanistes, certainly did not clearly indicate that he applied the specific name Mytilus discors to any other species than that to which it was applied by its original (in this case unnamed) author, so that the conditions under which the type species is to be treated as having been given a new binomen are not fulfilled (Copenhagen Decisions on Zoological Nomenclature, 1953: 68–9). It must be assumed that a taxonomist correctly identified the species referred to a new genus unless there are grounds for considering that the intended type-species was cited under a wrong name by mis-identification (Chester Bradley, 1957: 121, and references there quoted). I conclude, therefore, that the type of Lanistina Gray 1847, n. nov. for Lanistes Swainson 1840 (not of Montfort, 1810), is Mytilus discors Linnaeus, and that these generic names are synonyms of Musculus Röding.
I have pleasure in naming the genus after Dr. Tron Soot-Ryen, Director of Tromso Museum, Norway, in recognition of his valuable contribution to the systematics of the Mytilidae.
Ryenella impacta (Hermann)
1782. Mytilus impactus Hermann, Naturforscher, XVII: 152.
1843. Modiolarca (sic.) impacta (Hermann); Gray, in Dieffenbach's Trav. N.Z. II: 259.
1915. Musculus impactus (Hermann); Iredale, Trans. N.Z. Inst. 47: 484.
1933. Modiolaria impacta (Hermann); Powell, Rec. Auck. Inst. Mus. 1 (4): 183.
1940. Musculus impactus (Hermann); Powell, Auck. Mus. Conch. Club Bull. 1.
1946. Modiolaria impacta (Hermann); Powell, Shellfish of N.Z. (ed. 2): 57.
1955. Lanistina impacta (Hermann): Soot-Ryen, Allan Hancock Pacif. Exped. 20 (1): 74.
1957. Musculus impactus (Herman): Powell, Shells of N.Z.: 77.
This species occurs sparingly in Wanganuian sediments back to the Waipipian Substage of the Waitotaran (e.g., GS 4254, Waipipi) but the only earlier record is of Musculus cf. impactus from the Altonian Stage (Lower Miocene) of Waiheke Island, by Powell & Bartrum (1929: 400).
Genus Gregariella Monterosato
1884. Nomencl. Gener. Specif. alcun. Conchig. Medit.: 11.
Type (by subsequent designation, Crosse, 1885): Modiolus sulcatus Risso (non Lamarck) = M. barbatellus Cantraine = M. opifex Say 1825 (fide Soot-Ryen, 1955).
Soot-Ryen has synonymised the names Botulina Dall, Trichomusculus Iredale, and Tibialectus Iredale with Gregariella and this is accepted until systematic differences
of generic rank can be demonstrated. Tibialectus otteri Iredale is described as “found boring in coral” and Gregariella coarctata as “burrowing in the shells” of Spondylus and Murex, but it seems doubtful whether they are true borers or merely nestlers like G. opifex (Say), G. chenui (Recluz) and G. barbatus (Reeve).
Gregariella barbata (Reeve)
1858. Lithodomus barbatus Reeve, Conch. Icon. X. pl. 5, f. 27.
1913. Modiolaria barbata (Reeve); Suter, Man. N.Z. Moll. 864, pl. 63, f. 3.
1924. Trichomusculus barbatus (Reeve); Iredale, Proc. linn. Soc. N.S.W. 49: 196.
New Zealand specimens have not so far been distinguished from topotypes. Fossil records of G. barbata are from GS 4174, Rapanui Marine Sand at Wairoa Stream, Waipipi (Hawera Series), and from GS 5784, Opawe Stream, west flank of Ruahine Range (Hautawan Substage, Nukumaruan). Laws (1936) recorded Trichomusculus cf. barbatus from Kaawa Creek (Opoitian).
Gregariella lornensis (Laws)
1932. Trichomusculus lornensis Laws, Trans. N.Z. Inst. 62: 183, f. 41.
Lorne, North Otago (Kaiatan, Upper Eocene).
Gregariella n. sp.
1944. Trichomusculus n. sp., Laws, Trans. roy. Soc. N.Z. 73 (4): 298.
Pakaurangi Point (Altonian, Lower Miocene).
Genus Dacrydium Torell, 1859
Subgenus Quendreda Iredale
1936. Rec. Aust. Mus. 19: 271.
Type (by original designation): Dacrydium fabale Hedley.
Soot-Ryen (1955: 86) has used Iredale's name Quendreda as a subgenus of Dacrydium provisionally, noting that “the two grooved teeth and lack of a thickened support for the anterior adductor separate this group from typical species of Dacrydium” and has included a new species from the Galapagos Islands (D. (Q.) clegantulum Soot-Ryen).
Dacrydium (Quendreda) pelseneeri Hedley
This is a rare species and the type is perhaps not fully mature. Soot-Ryen noted that the New Zealand species seems not to have the grooved teeth of D. fabale, but it is otherwise so similar that it must be classed in Quendreda if Iredale's group-name is recognised; the grooved teeth may develop only in fully mature shells.
Powell (1957) lists D. pelseneeri only from the Aupourian Province (North Auckland) but he had earlier recorded it from off Puysegur Point, in the Forsterian Province (Powell, 1927).
A topotype of Dacrydium simulator Laws (Kaawa Creek, Opoitian, Pliocene) has been examined Its hinge, with chrondrophore, agrees quite well with that of Dacrydium, but shape differences suggest it is not closely related to D. pelseneeri.
Genus Crenella Brown
1827. Illustr. Conch. Great Brit. Ireland, pl. 31, f. 12–14.
Type (by monotypy): Mytilus decussatus Montagu, 1808. Recent, Boreal.
Crenella radians (Suter) (Fig. 6, 7 in text).
1908. Dacrydium radians Suter, Trans. N.Z. Inst. 40: 355, pl. 27, f. 11.
1913. Man. N.Z. Moll.: 872, Atlas (1915), pl. 51, f. 19, 19a.
Even Suter's poor figures suggest that this species is not congeneric with Dacrydium fabale Hedley and D. pelseneeri Hedley, the species with which Hedley introduced Dacrydium into the Australasian fauna Whereas Dacrydium has an internal resilium supported on a deep resilifer or chondrophore flanked rather symmetrically on either side by tooth-like thickenings of the hinge margin, D. radians
has an asymmetric hinge plate, with a sunken ligament behind the beak, and the anterior limb thickened to form a crenulated tooth-like process below the umbo, like Mytilus decussatus Montagu and other species classed as Crenella.
Two of Iredale's genera for Australian species are related to Crenella. Solamen Iredale 1924, based on S. rex Iredale, differs from Crenella in its finer radial sculpture and lack of a tooth-like process below the umbo (Soot-Ryen, 1955: 17). Exosiperna Iredale 1929, based on Arcoperna scapha Verco, is smaller, more elongate (as an adult), and has fine cancellate sculpture and a solider shell, judged by specimens in the New Zealand Geological Survey, sent to Suter by Verco. According to Iredale (1929: 166) Exosiperna does not show the hiatus in sculpture characteristic of Musculus and Crenella, but this character is variable in some populations of a single species These three genera are closely related and their status as yet uncertain. Dacrydium radians Suter more closely resembles the type of Crenella than either Solamen rex or Exosiperna scapha. Other southern species which may be related are “Crenella decussata Montagu” recorded from Burdwood Bank by Melville and Standen (1912) and Crenella marionensis E. A. Smith (1885) from off Marion and Prince Edward Islands.
Figs. 6, 7.—Crenella radians (Suter). Fig. 6—Lectotype (largest, TM 199), paralectotype (TM 200) and juvenile from 18 fathoms off Hen Island (smallest, TM 2138). Drawn to same scale to show change of shape with growth. Note hiatus between radially sculptured anterior and main parts of the lectotype. Fig. 7—Paralectotype (TM 201), showing hinge 38 fathoms, 5 miles south of Cuvier Island.
Crenella radians, like C. divaricata d'Orbigny (Peru to California), Solamen columbianum (Dall) (West Mexico to Aleutian Islands) and S. megas (Dall) (Panama) and Exosiperna scapha (Verco) (Southern Australia), tends to become more elongate as it grows (Fig. 6). The ribbing increases by bifurcation. Generally a rib broadens abruptly and a groove develops down the centre, but sometimes the rather distant concentric lamellae interfere and a new rib appears to arise by interpolation. A narrow smooth stripe or hiatus between the radially sculptured anterior and main parts of the shell is present in the lectotype (Fig. 6) but is absent in some paralectotypes from the same dredge sample.
Crenella radians seems to be a strictly northern (Aupourian) element in the living fauna and the genus has as yet no fossil record in New Zealand.
Stratigraphic Distribution of New Zealand Mytilidae
The annexed table summarizes the known distribution of Mytilidae in the series and stages of the New Zealand Tertiary and Quaternary, indicated by the conventional letter symbols at the heads of the vertical columns.
|Mytilus e. aoteanus||X||X|
|Trichomya n. sp.?||X|
|Amygdalum dolichum (?)||X||X||X|
|Botula (Notobotula) molina||X|
|Musculus (?) elongatus||X|
|Musculus sp. indet.||X||X|
|Gregariella cf. barbata||X|
|Gregariella n. sp.||X|
The Tertiary record is obviously very incomplete, doubtless owing to the scarcity of sediments deposited in the shallow depths and on the rocky bottoms which many mussels inhabit.
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Dr. C. A. Fleming,
N.Z. Geological Survey,