EXOTIC UNI0NID.4:. f^l 



very much larger. It belongs to the division which I made o^ symphynote Umonidce, 

 and this specimen is connate, having still part of the valves connected over the 

 ligament. 



MONOCONDYLCEA RHOMBOIDEA. PI. 42, fig. 143. 



Testa Ircvi, rhombo-quadratii, vald^ compressa, ad latere planulata, valdc inaequilaterali, p.istiee subalatfi, 



antic^ obliqu6 truncata ; valvulis tenuibus ; natibus vis prominentibn.s, ad apices crebrissirai^ et 



rainuti undulata ; epiderinide olivacea, striata, nitida, obsoletti radiata; dentibus eardiiialibus parvis, 



compresso-tubereulatis, in ntroque valvulis singulis ; marjrarita vol aurea vol purpurospcnto et vald^ 



iridesconto. 



Shell smooth, rhombo-quadrate, very much compressed, flattened at the side, 



very inequilateral, somewhat winged behind, obliquely truncate before ; valves thin ; 



beaks scarcely prominent, closely and minutely undulate at the tips; epidermis 



olive, striate, shining, obscurely rayed ; cardinal teeth small, compressed-tubercular, 



single in each valve ; nacre golden or purplish and very iridescent. 



Monocomh/Jnrn rhomhoiiha, Lea. Proc. Acad. Nat. Sci. 1859, p. 187. 



Hah. — Euphrates River, near Bagdad, Asia. G. Von dem Busch. M. D. 



My cabinet and cabinet of Dr. Yon dem Busch, Bremen. 

 Diam. -9, Length 2-8. Breadth 3-2 inches. 



Shell smooth, rhombo-quadrate, very much compressed, flattened at the sides, 

 very inequilateral, slightly winged behind, obliquely truncate before ; substance of 

 the shell thin ; beaks scarcely prominent, closely and very minutely undulate near 

 to the point of the tips ; ligament rather long, somewhat thin and light brown ; 

 epidermis olive, striate, shining, obscurely rayed and with one or two very distant, 

 broad marks of growth ; umbonial slope very slightly raised and scarcely rounded ; 

 posterior slope exceedingly narrow, raised into a compressed keel, slightly darker 

 than the rest of the disk, and with two rather indistinct rays on each valve from 

 the beaks to the posterior margin; cardinal teeth small, compressed-tubercular, 

 single in each valve ; anterior cicatrices distinct, rather large and moderately im- 

 pressed ; posterior cicatrices confluent, very large and very slightly impressed ; dorsal 

 cicatrices in a row below the centre of the cavity of the beaks ; cavity of the shell 

 very shallow and very wide ; cavity of the beaks exceedingly shallow and rounded ; 

 nacre golden or purplish, satin-like and iridescent. 



Remarks.— T\\\i^ is a very remarkable species and may be considered as altogether 

 a new type. Two opposing valves of different individuals of nearly the same size, 

 were sent to me by Dr. Von dem Busch. The two differ slightly in the color of the 

 epidermis, one being greenish olive with some rays, and the other brownish olive with 

 very indistinct rays. The marks of growth differ in one having a single broad, brown 

 mark, three-fourths of the distance from thp beak to the basal margin, and the other 



