Thomson. — Geology of Middle Waipara and Weka Pass District. 375 



Pachymagas marshalli (Andrew). (Fig. 7.) 



1906. Magellania marshalli Andrew, Trans. N.Z. Inst., vol. 38, 

 p. 456, pi. iv, fig. 3, a, h. 



The holotype is a poorly preserved, crushed, and somewhat distorted 

 specimen, from which one may nevertheless conclude that it was originally 

 a nearly suborbicular shell with short 

 beak, broad, slightly curved hinge-line, 

 rounded convex sides, and probably 

 a rounded front. The convexity is 

 slight, and the folding apparently 

 almost negligible, but in the direction 

 of incipient ventral uniplication. The 

 beak is erect, little produced above 

 the hinge-line, and possesses a mode- 

 rate mesothyrid foramen with well- 

 marked beak-ridges; Length of holo- 

 type, 49 mm. ; breadth. 48 mm. 



The dorsal valve was partially 

 ground down by Dr. Andrew to ex-* 

 pose the septum. The holotype is in 

 the Otago Museum. 



Type locaHty : Clarendon limestone, Fig. 1.—Pac7iymagas marshalli. Holotype. 

 Milbnrn Quarry, Otago. No speci- Natural size, 



mens are known from the Waipara 

 district. 



Smaller shells, up to 35 mm. in length, which agree closely in shape, 

 occur in the Moilnt Somers limestone, and the greensands of Curiosity 

 Shop, Kakanui, All Day Bay, and Three Roads. 



Pachymagas cottoni n. sp. (Fig. 8.) 



1908. Magellania sinuata Thomson, Trans. N.Z. Inst., vol. 40, p. 101, 

 pi. xiv, fig. 3 (not of Hutton). 



Shell broadly elliptical, with a beak of moderate length, a broad, slightly 

 curved hinge-line, nearly straight sides, and a rounded front. Convexity 



Fig. 8. — Pachymagas cottoni. Holotype. Natural size. 



moderate, anterior commissure with a broad shallow ventral sinuation, 

 flattened along the bottom. Beak erect, foramen moderate, mesothyrid, 



