1026 PELECYPODA. [Eulamdlibranchia. 



Length, 68 mm. ; height, 46 mm. ; diameter, 25 mm. 



Type in the collection Journ. de Conchyliologie ? 



Hob. North and South Islands, in sandy mud in sheltered bays, 

 from low-water mark to about 100 fathoms ; not common. Also 

 Australia and Tasmania. 



Fossil in the Pliocene. 



Fam. MYOCH AMIDES, DaU. 



Animal with short siphons ; a fourth pallial orifice present ; foot 

 small. 



Shell very inequivalve, free or sessile, solid, subnacreous, edentulous, 

 the dorsal margins of one valve overlapping those of the other, which 

 fit into corresponding depressions in the shell-wall ; ligament amphi- 

 detic, external or absent ; resilium internal, alivincular ; area arnphi- 

 detic or obsolete, a false area formed on each side of the beaks by 

 the flattened cardinal margin of the valves ; shell closed ; pallial 

 sinus small. 



Tertiary to Recent. 



Genus 1. MYODORA, Gray, 1840. 

 Myodora, Gray, A.M.N.H., iv, 1840, 30(3. Type : Pandora brevis, Sowerby. 



Shell free, inequivalve, compressed, somewhat flexuous, subequi- 

 lateral, triangularly ovate, rounded in front, contracted and truncated 

 behind, rather thin, white, nacreous within ; right valve more convex 

 than the left, which is usually flat ; resihum narrow, triangular, median, 

 internal ; furnished with a sickle-shaped ossicle (lithodesma), placed 

 below the resilium. Pallial impression sinuated posteriorly. 



Distribution. From the islands of the China Sea and the Philippines 

 to Australasia. 



Fossil in the Tertiary. 



KEY TO SPECIES. 



A. Shell transversely elongate. 



a. Shell subequilateral. Posteriorly broadly truncated ; 



interior with radial sulci . . . . . . pundorijormis. 



aa. Shell inequilateral. 



b. Anterior end shorter ; posteriorly broadly trun- 

 cated ; interior with 1 ray descending to front 

 of pallial sinus . . . . . . . - nntipodutn. 



bb. Anterior end longer ; posteriorly narrowly trun- 

 cated ; interior with 1 ray descending to the 

 upper part of the pallial sinus . . . . Boltoni. 



B. Shell triangular or subtriangular. 



a. Left valve slightly convex. Shell very solid, small, 



anterior end a little longer . . . . . . crassa. 



aa. Left valve flat or lightly concave. 



b. Shell equilateral ; posteriorly broadly truncated ; 



interior radially sulcate . . . . . brevis. 



bb. Anterior end a little longer ; posteriorly subtrun- 



cated ; interior with 2 radial rays . . . . novce-zealandiu'. 



