﻿EXOTIC UNIONIDJE. 263 



very much larger. It belongs to the division which I made of symphynote Unionida;, 

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

 ligament. 



MONOCONDYLGEA RHOMBOIDEA. PL 42, fig. 143. 



Testa laevi, rhombo-quadrata, valde cornpressa, ad latere planulata, valde inEequilaterali, postice subalata, 

 antice oblique truncata ; valvulis tenuibus ; natibus vix proniinentibus, ad apices crebrissime et 

 minute undulata; epiderrnide olivacea, striata, nitida, obsolete radiata; dentibus cardinalibus parvis, 

 compresso-tuberculatis, in utroque valvulis singulis ; margarita vel aurea vel purpurescente et valde 

 iridescente. 



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. 



Monocondylcea rhomboidea,. Lea. Proc. Acad. Nat. Sci. 1859, p. 187- 



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



My cabinet and cabinet of Dr. Von 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. — This 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 the beak to the basal margin, and the other 



67 



