Thomson. — Geology of Middle Waipara and Weka Pass Disfricf . 379 



but hardly so pronounced. Beak produced well beyond the hinge -line, 

 erect, foramen large, mesothyrid. attrite. Length of holotype, 44 mm. ; 

 breadth, 34mra. ; thickness, 25-5 mm. 



This species, though somewhat less folded than P. parki, is more convex, 

 and has a more prorhinent beak both as regards length and production 

 dorsally of the hirige-line^ 



Type locality : Foot of dip-slope, main Mount Brown limestone, Weka 

 Pass. The species is common in this limestone, and is unknown elsewhere. 



Imperfect specimens, believed to belong to this species, from the main 

 limestone between Mount Brown and the road, have a cardinal process 

 more prominent even than that of P. parki and comparable to that of 

 Neothyris ovalis. 



Pachymagas morgani n. sp. (Plate XXVII, figs. 4-6.) 



Shell broadly ovate, beak moderately short, hinge-line narrow, not much 

 curved, sides convex and rounded, tapering to a rather narrow produced 

 front. Valves moderately convex, the dorsal with a narrow, shallow, 

 median sulcus from about the middle, ventral with a broad rounded 

 longitudinal fold a'nd flattened sides, anterior commissure sloping on each 

 side to a moderately deep, rather narrow, flat-bottomed sinuation. Beak 

 suberect, not much produced dorsally of the ventral valve, foramen fairly 

 large, mesothyrid, attrite. Length of holotype, 47 mm. ; breadth, 41 mm. ; 

 thickness, 24 mm. 



This species is less strongly folded than P. parki, and has a narrower 

 hinge-line and more convex sides. It difiers from P. hectori in its narrower 

 and more produced front, due to' narrower folding. The cardinalia are 

 imknown. 



Type locality : Foot of dip-slope, main Mount Brown limestone, Weka 

 Pass, where it is moderately abundant. It is unknown outside the Waipara 

 district. 



Pachymagas coxi n. sp. (Plate XXVI, figs. 10-12.) 



Shell roundly ovate, beak of moderate length, hinge-line moderately 

 broad and curved, sides convex and regularly rounded, front rounded. 

 Valves moderately convex, anterior commissure with a broad, shallow, flat- 

 bottomed sinuation. Beak suberect, hardly produced dorsally of the hinge- 

 line, foramen large rela,tively to the size of the shell, mesothyrid, attrite. 

 Interior unknown. Length of holotype, 33 mm.; breadth, 29*5 mm. ; 

 thickness, 17 mm. 



This species, though smaller, agrees nearly in proportions of length 

 and breadth with P. morgani, but has a more rounded front and broader 

 folding. In these characters it agrees more nearly with P. hectori, but is 

 broader, attains its greatest breadth nearer to the hinge-line, and is less 

 convex. 



Type locality : Foot of dip-slope, main Mount Brown limestone, Weka 

 Pass. The species is fairly rare in the Mount Brown limestone, and has 

 not been identified outside the district. 



' Pachymagas huttoni Series. 



Pachymagas huttoni Thomson. (Plate XXVI, figs. 7-9.) 



Trans. N.Z. Inst., vol. 47,a915, pp. 395, 403, fig. 2, c. 

 This species has already been described, but the holotype has not been 

 figured, an omission I now rectify. 



