of Wairuna trig. N.Z.M.S. 1, Sheet S170 (Provisional Edition), Fossil Sample S170/628. Collected by B. L. Wood, N.Z. Geological Survey.

Diagnosis. Unusually high in outline, anterior dorsal margin high and steeply inclined. Beak narrow and prominent, hinge short. Byssal sinus in the left valve weak. Radial ornament very fine and discontinuous.

Dimensions (in millimetres).

Description. External: The shells are relatively high, with prominent slightly prosogyrous beaks, of which the umbonal angle measures approximately 60°. The anterior margin extends almost to the lower third of the height of the shell, and the ventral and posterior margins are well rounded, the posterior margin being most extended close to mid-height. Angle α measures 60°. The greatest width lies close to mid-length in the lectotype, and at the lower third in the right valve from GS 5156.

A deeply excavated false lunule lies in front of the beaks. The byssal sinus is well developed in the right valve, and is deeply excavated under the beak (Fig. 15). In the left valve the sinus is weak though long in the specimen from GS 5156, and is apparently weak in the lectotype.

The hinge is almost entirely posterior, and has a small posterior wing. A high triangular ligament area is visible in the specimens from GS 5156. The area is marked by weak growthlines and bears a triangular ligament pit. The anterior margin of the area projects forward as a low ridge.

The ornament comprises sharply defined concentric growth-lines and steps. Very fine radial filae are present between the concentric growth lines. About two or three filae occur in 1 mm at the ventral margin of the shell, measured at abòut 20 mm from the beak.

Internal Muscle scars are faintly defined. Both the posterior and anterior impressions lie at mid-height. The anterior scar is rounded in outline, and placed close to the anterior margin below the byssal sinus. The posterior scar is apparently elongated and crescentshaped. The impressions are linked by a low ridge with a groove on each side.

The posterior part of the ligament area is supported by a short buttress, at least in the left valve from GS 5156.

The shell is more than 2 mm thick at the central margin. Its structure is unknown.

Resemblances. One of the closest species is Mysidioptera a kittlii Bittner (1895, Pl. 21, Fig. 15), from the Ladinian Red Marmor of Han Bulog and Haliluci in Bosnia, and also the Schreyeralm-Marmor of the Northern Alps and the Anisian of the Dinarides M. kittlii closely resembles M. globularis in its well rounded outline, long anterior dorsal margin, and high ligament area. Moreover, the byssal sinus of the left valve is small in both species and the ornament predominantly concentric, with fine radial striae. M. kittlii can be readily distinguished by its more roundly inflated profile, its more incurved beak, longer hinge, and larger posterior wing.

Wilckens (1909) made M. kittlii the type species of subgenus Latemaria. The subgenus is supposedly distinguished from Mysidioptera by the incurved beak and globose shell, but these characters seem to be of minor importance, and it is doubtful if the subgenus is warranted.

The well-inflated species, M. globosa Broili (1930, Pl. 22, Fig. 16) of the Pachycardientuffe is another species referred to Latemaria by Wilckens (1909) Diener (1913, p. 110) compared a shell to the same species from the Carnian Myophoria Limestone of Kashmir M. globosa agrees with the New Zealand species in its prominent beak, long false lunule, and ornament, but the European species is more elongated in outline, and has a more incurved beak than that of M. globularis.

Age. The lectotype of M. globularis and another specimen mentioned by Trechmann come from beds below Manticula problematica in Nelson, and are presumably Oretian, unless they were not in place. The specimens from GS 5156 are from

Otamitan beds. They were mistakenly mapped as Oretian by Wood (1956), but the fauna includes the Otamitan key fossil, Manticula problematica.

Discussion. The specimens from GS 5156 were referred to Oretia by Marwick in Wood (1956).

Mysidioptera riceae n.sp. Figs. 8, 12–14, 16–20.

Named after Miss Mabel Rice, former Editor of the New Zealand Journal of Geology and Geophysics.

1939. ? Gonodon mellingi non Hauer Marwick in Ongley: 40 (list).

1958. ? Atomodesma Grindley: 43.

1960. Mysidioptera n.sp. Grindley and Waterhouse: 262.

Holotype. External cast of the left valve, with the hinge and most of the internal cast, specimen TM 2101. Fig. 20.

Type Locality. GS 1431, Waiwera River, 20 to 30 chains below hairpin bend, N.Z.M.S. 1, Sheet S179 (Provisional Edition), Fossil Sample S179/475. Collected by M. Ongley.

Measured Specimens. TM 2096–7; 2101–2109, 2148, N.Z. Geological Survey.

Material. This species is represented in the collections at the Geological Survey by a few valves from a number of localities, and by nine specimens from GS 928.

Localities See Table I.

Diagnosis. Moderately small shells. Usually slightly higher than long, anterior dorsal margin high and steeply inclined. Beaks anterior, moderately prosogyrous, inconspicuous. Umbonal angle close to 90°. Posterior wing poorly developed. Byssal sinus wide in both valves. Ornament of strong concentric wrinkles and subordinate fine radial filae. Ligament area short and high.

Description. External: The shells are moderately small for the genus. They are probably equivalve or nearly equivalve. Only one specimen with valves conjoined is available, and in this the right valve appears to be a little more inflated than the left, but the specimen is slightly distorted. The zone of maximum inflation is inclined at 45° from the hinge.

The beaks are placed well forward near the anterior fourth of the shell length. They are moderately prosogyrous, and curve towards each other over the hinge, without projecting above the dorsal margin. The umbonal angle ranges from 75° to 110°, and is usually more than 90°. From the beak the anterior margin sweeps with marked concavity to below midheight, and the ventral anterior, ventral and posterior margins are well rounded. Virtually no posterior wing is developed along the dorsal margin.

In front of the beaks is a wide and deep false lunule, defined by a weak beak ridge and ornamented by strong concentric growth ridges. A byssal sinus is present in both valves. That of the right valve is deeply notched immediately in front of the beak and ligament area.

Low concentric growth ridges and steps lie over the shell, crossed by fine radial filae. About three filae occur in 1 mm at 20 mm from the beak.

The ligament area is less than half as long as the shell. It is triangular, deep-set, and between a fifth and a sixth of the shell in height. The anterior edge of the ligament area projects slightly in a sharp ridge in front of the beak. The surface of the ligament area is marked by horizontal and faint vertical striae, and one or two steps of growth. A shallow, triangular resilifer slopes obliquely over the area from the beak posteriorly to the hinge margin.

Internal: In most shells the inner shell below the anterior margin of the ligament area is slightly thickened and reflected to form a small triangular shelf.

Muscle scars are moderately impressed. The posterior scar lies close to the posteriormargin at about the upper third of the shell height, and is somewhat oval in shape, with a straight anterior margin. The anterior scar lies at the lower third, near the lower end of the false lunule, and is more rounded in outline. In some specimens it is raised. The two scars are linked by a simple pallial line.

The shell is as much as 2 mm thick at the anterior margin. In appearance it is platy, like that of an oyster. A thin section of a slightly decorticated specimen showed that the shell is composed chiefly of confused crystals of calcite, possibly recrystallized from aragonite. A thin inner layer .5 mm thick is comprised of crossed lamellae, and a thin outer layer .5 mm thick is comprised of clear homogeneous calcite. Another valve has a layer of crossed lamellae 1 mm thick.

Variation. Insufficient specimens are available from any one locality to enable the variation within the species to be adequately studied. Most specimens are similar to the holotype in outline, but the length:height ratio, and the length of the hinge vary slightly. The umbonal angle varies in specimens from one locality, and in some specimens the beak overhangs the ligament area more considerably than usual. Strong concentric undulations are developed in some shells (Fig. 19), but other specimens from the same locality are comparatively smooth.

Resemblances. M. riceae is distinguished from other non-costate species of Mysidioptera by the wide umbonal angle, low umbo, poorly developed posterior wing, and wide byssal sinus in both valves.

The new species resembles M. globularis (Trechmann) in size, poorly developed posterior wing, short hinge line, and ornament. It is distinguished from globularis by the more elongated outline, and the more prosogyrous broader beak that possibly projects less about the hinge. In the left valve of riceae, the byssal sinus is better defined, and no buttress is developed under the hinge. These differences are slight, and riceae may prove to be a subspecies or variety of globularis.

An indeterminable specimen figured by Diener (1913, Pl. 12, fig. 13) from the Lower Muschelkalk (Anisian) beds of Kashmir is close to the new species in outline. Like M. riceae this specimen has a low beak, a long anterior dorsal margin that is steeply inclined from the hinge, and a rounded outline. The ornament comprises concentric lamellae. The Kashmir form is distinguished from the New Zealand species by the larger, less prosogyrous beak, larger posterior wing, and entire lack of radial ornament. The depth of the byssal sinus is unknown in the Kashmir shell. Possibly the Kashmir shell is conspecific with M. exima Diener (1913, Pl. 11, fig. 8) from the same horizon. M. exima is distinguished from M. riceae by its large size, small byssal notch and lack of radial ornament.

A large right valve associated with Manticula problematica (Zittel) in Carnian beds of New Caledonia was compared with M. exima by Avias (1953, Pl. 23, Fig. 4). The New Caledonian shell is well inflated, lacks radial ornament, and is very large, but shows some similarity in outline to the New Zealand species. Unfortunately the details of the hinge and byssal sinus are not described.

A less elongated shell with a steeply inclined anterior-dorsal margin, low beak, and small posterior wing is the chiefly Ladinian species M. vixcostata (Stoppani) of Europe. Bittner (1895, Pl. 20, Figs. 24–28) figured the species as M. cf. and aff. vixcostata Stoppani, and Broili (1903, Pl. 20, Figs. 17, 18) recorded the species as M. incurvostriata (non Woehrmann, fide Cox, 1924). Cox (1924) has described the species from the Carnian of Jordan. Costae are stronger than in the New Zealand form.

The Ladinian and Carnian species, M. woehrmanni Salomon (1895, Pl. 5, figs. 15–17; Bittner, 1895, Pl. 20, figs. 7–10; Broili, 1904, Pl. 20, figs. 12–14) from Italy, Sicily and the southern Alps of Europe, is somewhat similar in outline to elongated specimens of the new species. The European species is distinguished from M. riceae by its slightly protruding beak, and by its short anterior-dorsal margin that is less steeply inclined from the beak. Moreover the byssal notch of the European shell is less well defined. No radial ornament is present.

Two supposed varieties of M. ornata Salomon from the Ladinian Esino beds are moderately similar to the new species in outline. These are var. lombardica Bittner (1895, Pl. 21, fig. 13) with weak radial ornament, and var. laevigata Bittner(1895, Pl. 21, fig. 12) with a deep byssal sinus and no radial ornament. The varieties have similar low, but less prosogyrous beaks than the new species, and the anterior-dorsal margins are shorter.

Like the New Zealand form, M. obliqua Broili (1903, Pl. 22, figs. 13, 15) from the Pachycardientuffe, and also reported from the Ladinian by Wilckens (1909), is a well-rounded and moderately well inflated species, with weak radial ornament. However, the anterior dorsal margin of M. obliqua is short, and the beak is more prominant than in M. riceae.

Discussion. Specimens from the type locality GS 1431 were tentatively referred by Marwick in Ongley (1939) to a species from Nugget Point that was identified as Gonodon mellingi Hauer by Wilckens (1927). The specimens from Nugget Point lack the wide byssal sinus and well defined false lunule of Mysidioptera.

A specimen from GS 6043, Eglinton, was mistaken for Atomodesma by Grindley (1958). It is recorded as Mysidioptera n.sp. by Grindley and Waterhouse (1960).

Occurrence. M. riceae is a rare to frequent species in Otamitan beds, and is commonly associated with Manticula problematica (Zittel). It occurs in the North