Zelandites n. gen.
This genus is suggested for some ammonites that could not be placed in any of the genera of which detailed descriptions and literature were available. The ornamentation is so similar to that of several species of Gaudryceras that it seems necessary to place it close to that genus. The narrow and high whorl has the general form of that of Gaudryceras varuna, which has been recorded from Quiriquina by Steinmann as well as from its original locality. On the other hand, the suture-line, so far as its general appearance is concerned, and especially in the nature of the first lateral lobe, is so peculiar that it becomes doubtful if the species should be included in the Lytoceratidae. However, in the absence of specimens of allied species for comparison, and of more extensive literature, it has been placed here provisionally.
Ammonites varuna Forbes (1, p. 107, pl. 8, fig. 5).
Ammonites varuna Forbes, in Stol. (11, p. 111, pl. 58, fig. 1).
Desmoceras kawanoi Jimbo (22, p. 28, pl. 1, fig. 7 a, b).
Lytoceras (Gaudryceras) odiense Koss. (28, p. 129, pl. 18, fig. 1 a-c).
Lytoceras (Gaudryceras) varuna Forbes, in Koss. (28, p. 130, pl. 16, fig. 4 a-b: pl. 17, fig. 8).
Lytoceras varuna Forbes, in Steinmann (26, p. 84, Taf. 5, fig. 2 a, b; text-fig. 7).
Gaudryceras kawanoi Jimbo, in Yabe (37, p. 41).
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|Height of last whorl||12||48||8||44||12||53||13.5||52|
|Width of last whorl||7.45||30||6.5||35||7.5||33||7||27|
A, B, Zelandites kaiparaensis n. sp., Bull's Point, Kaipara Harbour, N.Z.; C, Lytoceras (Gaudryceras) varuna Forbes, in Koss. (28, p. 161); D, Lytoceras varuna Forbes, in Steinmann (26, p. 84).
The dimensions show a fairly close resemblance to Gaudryceras varuna, though the whorl of the New Zealand species is not so high and the umbilicus is a good deal wider.
Shell small, discoidal, with an involution of about two-thirds. The greatest width is just above umbilicus, to which the slope is steep, though it rounds off gradually at top of wall; thence the flanks slope gradually to periphery, which is narrow and sharply rounded. Body-chamber has the length of two-thirds of a revolution. Surface of inner whorls covered with fine hair-like ribs, at first strongly inclined forwards, but at top of umbilical slope they become straight and pass straight over periphery. Body-chamber has the same ornamentation as inner whorls. Nine deep constrictions in a whorl. They are at first radial in direction, but soon take a strong bend forward, and near periphery become radial again, passing over it with a barely noticeable backward curve. These constrictions are visible on the shell and have no ribs before or behind.
Suture-line peculiar, and the absence of much literature makes it hard to classify the species. The median saddle is sharp and has a few jags on side. External saddle high and bifid, with a much larger development on external than on internal side. The two lateral saddles are also bifid, but are much smaller, and seven auxiliary saddles can be distinguished. All divisions of the saddles have deep and sharp jags, which give rather a distinct appearance. External lobe about as deep as first lateral lobe, and rather wide. First lateral lobe wide, and the small secondary saddle in the middle is much less conspicuous and important than in Gaudryceras. There are larger projections on either side of it, and of these the internal one is by far the largest element in the whole. This is similar to the same lobe in Diplomoceras cylindraceum Defr. (47A, fig. 1259; 45, Taf. 45, fig. 47) and to that in D. wakanene, figured in this paper (Plate 19, fig. 3), but it is quite different from that in the four Indian species of Anisoceras Pictet = Diplomoceras Hyatt figured by Kossmat (28, Taf. 19). The other lobes present no unusual features. Auxiliary lobes and saddles highly inclined, and form a deep umbilical lobe. Internal portion of suture-line not much different from that of G. semileve or G. propemite, or of G. varicostatum van Hoepen, and approaches that of G. varagurense as drawn by Kossmat. In the three first-mentioned at least it may be said that there is a single wide and rapidly thinning saddle, which is high, while smaller saddles are represented by projections on its outer side. This is certainly distinct from the single thin and high saddle of G. subsacya and G. vertebratum as drawn by Kossmat.
The form of this species shows affinities with that of G. varuna and G. kawanoi, while the ornamentation is similar to the general characters of that of Gaudryceras.
Four specimens, all of them from Bull's Point, on the Kaipara Harbour. A specimen of a closely allied species is in the collection of the New Zealand Geological Survey. It was found by McKay at Awanui, near East Cape, in Cook County. It differs from the Kaipara form in ornamentation, as it is almost destitute of ribs, but in form and suture-line it differs but little.