62 



Dimensious '. — 













LcngtH. 



Width. 



Thickness or Ucptli, 



Hinge-line. 



If) mrn. 



26 



mm. 



14 mm. 



17 



mm. 



20 mm. 



27 



mm. 



I y mm. 



13 



mm. 



3 1 mm. 



27 



mm. 



1 5 mill 



13 



mm. 



22 mm. 



27 



mm. 



14 mm. 



12 



mm. 



23 mm. 



2S 



mm. 



17 mm. 



13 



mm. 



23 mm.+ 



32 



mm. 



18 mm. 



15 



mm. 



Remarks : 



— 1 here seems to be 



a somewhat wide range 



ot variation in the 



relative length 



of the hinge 



-line, but 



in all other points the 



shells 



possess re- 



lative dimensions tiuite similar to those of specimens from the other localities. 

 However, the forms reported by WEL[.t:i< do not seem sufficiently well pre- 

 served to be taken into comparison. 



There is a species of the genus made known to science from the Central 

 Himalaya by Cowper Rekd, namely Trif^kcia iiiicata Salter sp. It was 

 originally described from the Northern Himalaya as OrtJiis uncata by the 

 latter author, but is now referred to Hall's genus by Ri-:ed on reasonable 

 grounds. From this Hu-pei form is distinguished by several remarkable dif- 

 ferences. The former is much less transverse in outline, or rather circular, 

 with a median sinual depression on the ventral valve which is traceable very 

 close to the beak region. Reed observes, " The fine radial stri;E described 

 by Salter are not usually visible on the outer surface, but are in some cases 

 traceable on the inner lamin;e.'^ " The reason why radial strins, though faint, 

 are drawn in the figures given by him is thus made clear. 



Weller includes in the species now under consideration another form 

 from Lean-shan, Poraiiibonitcs intercede iis Martelli (non P.andek). An 

 examination of some figures of the latter species, as for instance, those g.ven 

 by Davii^so.s:,^^ inclines the present writer also to agree with the American 

 paleontologist. The difference in form of the two fossils, one of Martelli 

 and the other of Pander, is too conspicuous to be disregarded. The fine 



1) C. R- EP:— Ordovic. and Silur. Fossils from the Central Himalayas. Palatontologia 

 Indica, XV., vol. VH., 2. p. 30. 1912. 



2) T. Davi:).son: — Monogr. Brit. Fossil Brach., HI., p. 195. pi. XXV., etc. 1864—71. 



