Lobothyris richardsi n. sp.

Fig. 13, 1–17, 14A–D.

Holotype. BR 3286, a double-valved shelly specimen, slightly distorted, from R15 /f8585, GS 6754, south of Arataura Point, Kawhia. Collected by H.C. Arnold.

Derivation of name. This species is named for Marcus Richards of the Geology Department, University of Otago.

Material. The data series consists of 42 specimens, 8 from the Kawhia Syncline, 26 from the Taringatura Hills locality E45/f6635, and 8 from other Southland Syncline localities. 41 of these yielded valid measurements .

Kawhia Syncline. South of Arataura Point, Kawhia: R 15/f8585 (GS 6784). North Marokopa Coast: R 16/f8650 (GS 10037), R 16/f6896 (GS 10007), R 16/f8698 (? GS 10009). Marokopa: R 16/f0337 (AU 12074), R 16/f8638 (GS 9993). Awakino Gorge: R 17/f8574 (AU 341), R 18/f6582 (AU 326).

Southland Syncline. South Taringatura Hills: E45/f6635 (JDC 241). Benmore railway cutting: E45/f9578 (? JDC 730). Taylors Stream—Otapiri: E45/f073 (McF E29), E45/f0279 (JDC 4059) E45/f9462 (? GS 359), E45/ f9621 (JDC 1295), E45/f9910 (JDC 2095). Reaby Downs, Otamita Valley: F45/f0217 (E. Wright coll.).

Description. Medium-sized terebratulide with elongate, rounded-triangular outline and a straight to slightly convex anterior margin. Both valves are moderately inflated, the ventral valve generally more so. The dorsal valve on some specimens has a broad, shallow flat-floored fold involving almost full width of valve, but there is no definite sulcus. The anterior commissure is deflected by shallow uniplication. The shell exterior is generally smooth, with fine, irregular growth lines. The shell is densely and coarsely punctate.

In the ventral valve the beak is small, erect to suberect, with a rounded tip. The foramen is small, round, epithyrid, and surrounded by a short pedicle collar (Fig. 13.3a, 13.15c, 14A, D) Deltidial plates are small and conjunct (Fig. 14A). The beak ridges are sharply rounded (Fig. 13.9c, 14C). There are no dental plates.

In the dorsal valve the hingeplate is short, narrow and triangular, with a small narrow cardinal process (Fig. 14B, D). There is no median septum. Muscle scars are poorly shown on the dorsal valve of some specimens (Fig. 13.10a, 14C).

Dimensions. Dimensions of the holotype and representative specimens, and statistics for all measurable specimens are shown in Table 4. A length vs width graph is shown in Fig. 9C.

Range and Distribution. Small specimens are common at one locality in the South Taringatura Hills (E45/ f6635), which is early Otapirian.All other material comes from the late Otapirian. The species has a wide distribution from Kawhia to Awakino in the Kawhia Syncline, and in the latest Otapirian part of the Taylors Stream – Otapiri section (Southland Syncline), where it is found with Zeilleria spiculata . It does not extend into the Aratauran.

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Remarks. This species is included in Lobothyris on its shape and internal characters.

The straight anterior margin and small beak distinguish this species from the Jurassic Lobothyris simesi . It has a similar shape to the Siberian species L. monstrifera Dagys (see Dagys 1963, pl. xxv11 4 – 6), but that species is generally more convex.

L. cf. monstrifera is recorded from Alaska (Blodgett and Clautice 2000, Sandy 2001), but Sandy (2001) comments that “serial sections indicate internal differences between this form and typical Lobothyris and it is thought to represent a new genus” (p. 397).