14.7 



hinge ; ligament in connection ivith a curved shelly appendage or 

 ossicle. 



De Roissy's Chamostrea, better known amongst conchologists as the 

 Cleidotharus of Stutchbury, is a mollusc of somewhat anomalous character, 

 of which only a single species, inhabiting New South Wales, is known. 

 It has a shell like Chama, with the umboes spirally involute, and like that 

 genus it dwells attached firmly to the rocks, or in clusters one upon an- 

 other ; but the ligament is internal, and it is furnished with a detached 

 shelly appendage or ossicle similar to that of the genera of Myaria among 

 which it is arranged. The animal has been examined by Mr. Hancock, 

 and his observations go to confirm the correctness of this arrangement. 

 Internally the shell is lined with a greenish silvery-pearl, externally it is 

 tinged with yellow and brick-red. 



Figure. 



Chamostrea albida. PL 41. Tig. 224. Shell placed on its flattened 

 attached side, with the involute umboes nearest the observer. 



Genus 2. MYOCHAMA, Stutchbury. 



Animal ; mantle-lobes united ; pedal opening and siphons sur- 

 rounded by separate areas ; siphons distinct, unequal, small, 

 slightly fringed ; foot small, conical. fHancock.J 



Shell ; inequivalve, attached by the right valve to shells or stones, 

 and modified by form of surf ace of attachment ; left valve gib- 

 bous ; hinge composed of two diverging central teeth in each 

 valve, enclosing a cavity for the ligament, connected with which 

 is a shelly appendage or ossicle. 



Myochama is another remarkable ossicle-hinged parasite peculiar to New 

 South Wales, of which the animal has been described by Mr. Hancock. 

 The shell is, however, very different from that of Chamostrea. It is much 

 smaller, not stout and involutely spired, but ovate and slight, having its 

 surface modified in growth according to the irregularity of the surface 

 upon which it is attached. Mostly the Myochama are found adhering to 

 Trigonias, and although the upper valve is free, yet being formed symme- 

 trically along with the under or adhering valve, it partakes of the same 

 ribbed structure which is imparted to the adhering valve by the ribbed 



