262 CEETACEOUS PELECYPODA 



List of cretaceous species. 



Pictet and Campiche, Pal. Suisse.,, 4™^ ser.^, 3"^® part.^ p. 296, only record the following 

 two species under the name Biplodonta : — 



1-2. — Mysia UrgonensiSj P. and C.^ and M. gurgitisy P. and E. ; the first is from the Urgonien^ 

 the second from Gault-heds. 



In the list of the species of Lucina, I have particularly noticed the following as externally 

 resembling Mynm: — L, glohiformis, Leym., L,^ solidula, and i/. Turonensis -, the hinge-teeth of 

 these species should be carefully examined. 



3-5. — Mysia gibbosa, Gabb^ (Jour. A. N. Sc.^ pi. iv; p. 302), M. parilis, Con., (ibid. p. 278)^ 

 and / M. polita, Gabb^ (Pal. Calif.^ i^ p. 178 J are noticed from North America. 



6. — Hippagus Aemilianus is the only species which represents this family in the South Indian 

 cretaceous rocks. 



I may also notice that Cyprimeria obesa, which d''Orbigny described as a Lucina (vide p. 180)^ 

 has the external form and the hinge-teeth somewhat resembling those of a Psathuray but in the 

 only right valve which I have seen the anterior bifid cardinal tooth is much more oblique than in 

 Deshayes'' typical Psathura. However^ better preserved specimens of both valves would deserve 

 a careful comparison regarding this point. 



HIPPAGUS, Lea, 1833, (seep. 260). 



1. HiPPAGUS iEMiLiANUS, StoUczka, PL XIV5 Pig. 6. 



jH". testa verticaliter ovali, multo altiore quam longa, valde inflata, umhonihiis 

 ohtusiusculis, prominuUs, incurvis, approximatis instruct a, crassiuscula, stib-vitrea, in 

 siiperficie striis minutissimis sub-lamellosis concentricis ac alteris snh-obsoletis 

 radiantibus ornata ; regione lunulari et areali hand circumscriptis ; cardine edentido 

 obsolete insinuato ; margine interno continuo, levi. 



Height of shell : its length ... ... ... 1-44 



Thickness (of both valves) : „ ... ... ... 1*26 



I have already noticed that this species most closely resembles the eocene 

 IL isocardioides, Lea, the type of the genus, which is only a little higher and 

 apparently somewhat shorter than our fossil. The shell itself is of considerable 

 thickness, and of a silky appearance, as commonly seen in recent species of M/sia ; 

 the surface is covered with numerous striae of growth, some of which are stronger 

 than others, and towards the margin are intersected by deeper furrows ; besides 

 that there are numerous fine short interrupted radiating strige perceptible. 



i:o(?<^Zi^^.— Stripermatiir in whitish soft sandstone, in which a few specimens 

 only were discovered by the lamented Ch. ^milius Oldham, late Deputy Superin- 

 tendent of the Madras party of the Geological Survey of India. 



Formation, — Arrialoor group. 



