80 DESCRIPTIONS OF 



umbonial slope, has one impressed line only on the posterior slope of each valve, is 

 smaller and more delicate, is more compressed on the side, and the color of the 

 epidermis is not so green and shining. 



MONOCONDYLCEA PLANULATA. PI. 42, fig. 142. 



Testa alata, laevi, obovata, valde compressa, ad latere planulata, valdfe inaequilaterali, postice obtuse 

 angulata, antice rotunda ; valvulis tenuissimis, pellucidis ; natibus vix prominentibus ; epidermide 

 minutissimfe striata, luteola, postice subnitida, obsolete radiatS.; dentibus cardinalibus parvissimis, 

 compresso-tuberculatis, in utroque valvulo singulis ; margarita cEeruleo-alba et iridescente. 



Shell winged, smooth, obovate, very much compressed, flattened at the sides, very 

 inequilateral, obtusely angular behind and rounded before; valves very thin, 

 diaphanous; beaks scarcely prominent; epidermis most minutely striate, yellowish, 

 somewhat shining, obscurely radiated ; cardinal teeth very small, compressed, tuber- 

 culate and single in both valves ; nacre bluish white and iridescent. 



Monocnndylaa planulata, Lea. Proc. Acad. Nat. Sci., 1859, p. 187. 



Hah. — Java. G. Von dem Busch, M. D. 



My cabinet and cabinet of Dr. Von dem Busch. Bremen. 

 Diam. -5, Length 1'2, Breadth 1-9 inch. 



Shell winged, smooth, obovate, very much compressed, flattened at the sides; 

 very inequilateral, obtusely angular behind and rounded before ; substance of the 

 shell semi-transparent ; beaks scarcely prominent, apparently without undulations at 

 the tips ; ligament long, thin and concealed ; epidermis most minutely and trans- 

 versely striate, somewhat shining, yellowish, very obscurely radiated, on the posterior 

 slope green, with scarcely visible marks of growth ; umbonial slope slightly raised 

 and slightly rounded ; posterior slope pale green, narrow, raised into a compressed 

 wing enclosing the ligament and slightly wrinkled ; cardinal teeth very small, com- 

 pressed, tuberculate and single in both valves ; anterior cicatrices confluent, slightly 

 impressed, rather large ; posterior cicatrices confluent, very slightly impressed and 

 large ; dorsal cicatrices in a row across the cavity of the beaks and very slightly 

 impressed ; cavity of the shell very shallow and wide ; cavity of the beaks very shallow 

 and subangular ; nacre very thin, bluish white and iridescent. 



Remarks. — A single specimen only of this small, very much compressed and 

 delicate species was received from Dr. Von dem Busch. The beaks are slightly eroded 

 and may have possessed delicate undulations at the tip, but none are visible on this 

 specimen, which in every other respect is perfect. Its green posterior slope, its yellow 

 sides and fine strioe distinguish it from all other Monocondyloem with which I am 

 acquainted. In outline it is nearest to M. Gumingii, (nobis), but it is a much 

 smaller species, is much thinner, lighter, and is yellow while the other is brown. 

 This specimen may not have obtained its full growth, but I doubt if it ever grows 



