OF SOUTHEEN INDIA. 63 



cliaracter would not differ from Tellinomya, but though the description of the species 

 is not very clear, it appears to say that there is a special groove or pit under the 

 umbones for the reception of a spongy cartilage. An external ligament has not 

 been observed. Giebel (Abhandlungen Nat. Ver. fiir Sachsen und Th., vol. i, 

 1856-58, p. 105), describes a triassic Tell, edentula which may belong to this 

 genus ; it has apparently a cartilage-pit below the beaks. 



8. Corimtja, Ag., 1842, (Etud. crit., Mon. des Myes, p. 262). Shell very 

 thin, nacreous, slightly inequivalve, with one or usually two long ribs running from 

 the beak posteriorly ; hinge edentulous, margin of the shell behind the beaks 

 very slightly thickened, but not bent inside ; posterior muscular impression 

 distinct, elongated near the middle of the posterior margin ; pallial line indis- 

 tinct, beaks entire ; a thin ligament externally is very probably pi-esent. These 

 characters appear to me to justify the separation of CoHiitija from Thracia, and it 

 would seem as if the former were the mesozoic representant of the latter. Agassiz 

 when proposing the new genus was evidently led to it more from the general 

 characters, such as the shell-structure, than from any details relating to the hinge. 

 He merely says that the hinge is probably edentulous, but as the form of the shell 

 does not exhibit any marked difference from Thracia, it was united with this genus 

 by Deshayes, Terquem, and others. I cannot vouch for the statement that all 

 the species described by Agassiz under the name of Corbwja belong to that genus; 

 some of them may possibly be Thracm. The first species of the genus, Corimya 

 pingiiis, of which I have compared several tolerably well-preserved specimens, 

 exhibits all the characters which I have pointed out above. The posterior inter- 

 nal ribs recall Fandora, but I have not observed any groove for the attachment 

 of the cartilage. A large number of the species knowTi belongs to the Jurassic 

 period, but there are a great many well-marked types to be found also in cretaceous 

 beds, as I shall subsequently notice in detail; two species occm- in our South 

 Indian deposits. 



9. Axinus, Sow., 1821, (Min. Conch., vol. iv, p. 11). Shell rather thin, 

 anterior side short, rou.nded, posterior slightly move compressed, produced, with the 

 area somewhat excavated, and a long cartilage (?) groove along the entire upper 

 margins; no other hinge-teeth are known to exist. Sowerby considers Ax. angu- 

 latus from the London clay as the type of the genus, which has been by some 

 authors identified with Turton's Lepton, but I do not see from the existing mate- 

 rials sufficient reason for this. Sowerby's type species indicates a greater relation 

 to Thracia than to any other shell I know, and unless this typical species has been 

 properly examined and its characters better defined, it is useless shifting it to, or 

 identifying it with, another genus. M'Coy in his carboniferous fossils of Ireland, 

 p. 63, refers to Axinus a number of species apparently belonging to Dolabra, 

 Anodonlopsis, and similar allied genera which will be noticed subsequently. 



10. Thracia, Leach, 1824. Shell usually rather inflated, inequivalve, more 

 or less solid or thickened, scarcely nacreous internally, edge behind the beaks bent 

 in and prolonged internally into a small cartilage process ; pallial sinus broad and 

 ileep. — Eossil species belonging to Thracia proper are as yet only known from 



