OF SOUTHERN INDIA. 61 



The animal of Myocliama in general resembles that of Myodora, and equally 

 so the shell, esj^ecially as regards its thin structure and the form of the hinge. Al- 

 though it lives attached to foreign objects, it is impossible to find anywhere else 

 a better place for it. Some authors (Homer and others) have proposed a special 

 family to include Chamostrea and Myocliama. But when comparing the two shells, 

 tlieir form and the character of the hinge are so totally different that it seems quite 

 unnatural to class them together. Certainly Myocliama is much more allied to 

 Myodora (of which it must be considered as an aberrant form), than it is to 

 Chamostrea. 



Conrad quotes only four recent species from the Australian seas, and some 

 doubtful forms occur in the upper tertiary beds of Europe. The only shell, des- 

 cribed from older formations, which has an external resemblance to the recent 

 J/?/oc/«a?/ia, is Lycett's Oolitic JPtychomya Agasslzii (Proc. Cottesw. Nat. Club, I, 

 p. 69, pi. II, fig. 6). Lycett does not state whether both valves of the shell had 

 been found, but the one which he figaires is certainly externally very much like 

 the smaller and free valve of a Myocliama. The hinge is believed to be edentulou.s, 

 and if this be really the case the valve under description may also be a lower valve 

 of an Aiiomya. Lycett's statement requires confirmation on this point, before Ave 

 are able to say anything definite about the characters of that supposed Ptychomya. 



2. Myodora, Gray, 1840. Shell subtrigonal, posteriorly truncated ; right 

 valve more or less convex, its hinge with two diverging teeth enclosing the cartilage, 

 left valve flattened with two grooves at the beak ; ossicle free, rather large ; pallial 

 sinus small and broad. — The species of this genus are almost only known from the 

 Eastern and Australian seas ; the unequal form of the valves and the position of 

 the cartilage strongly remind us of Myocliama. 



3. Pandoi^a, Brug., 1792. Shell ovate, inequilateral, compressed, posteriorly 

 narrowly produced ; right valve smaller and flatter than the left one ; hinge with 

 an anterior more or less prolonged rib in each valve ; cartilage in a groove posterior 

 to the tooth, more or less adjacent to it ; no ossicle present ; pallial sinus very small. 

 Carpenter (Proceed. Zool. Soc, 1861, p. 601,) restricts the genus Fandora to the 

 species of the tyi^e Pand. imequicalvis fimequalis 1J Linn., rostrata. Lam., 

 P. p na, Penn., ohtusa, Lamarck. 



3«. Kennerlia, Carpt., 1861, (Proc. Zool. Soc, Lond., p. 602). Under this 

 name Carpenter separates a few species, which still more resemble Myodora, than 

 the true PandorcB. They all have a thin ossicle, and the typical species have radiat- 

 ing ribs on the right valve. Pand. (Keim.J bicariiiata. Carpenter, is the type of 

 the sub-genus. 



1. Cceiodon, Carp., 1861, (ibid., p. 599). The form of the shell is similar to 

 that of Pandora ; each valve with two hinge-teeth directed towards the anterior 

 adductor muscle, and in the left one they are connected by a thin lamina ; no ossicle 

 or pallial sinus. 



5. Clidiopliora, Carp., 1864, (ibid., p. 596). Similar in form to the last ; right 

 valve rather tumid, with three hinge-teeth ; the posterior one elongated ; left valve 



