CHIEFLY OF THE UNITED STATES. 2c3 



and minutely undulate at the tips; epidermis dark brown, cardinal teeth small, erect 

 and compressed ; nacre bluish-white and iridescent. 

 Proc. Acad. Nat. Sci. 1864, p. 286. 



Hah. — Near Mardin, in a stream foiling into tlie Tigris River, Asia, C. M. 

 Wheatlej. 



jVIy cabinet and cabinet of Mr. Wheatley. 

 Diam. -9, Length TG, Breadth o-l inches. 



Shell smooth, arcuate, very inequilateral, compressed at the sides, rounded before 

 and behind ; substance of the shell thick, thicker before ; beaks a little prominent, 

 recurved and minutely undulate at the tips ; ligament large, long and dark brown, 

 with rather distant marks of growth ; urabonial slope rounded ; posterior slope 

 narrow, slightly raised, with two slightly impressed lines in each valve from the tips 

 to the posterior margin ; cardinal teeth small, erect, compressed, inclining to be 

 double in the left valve, the cleft being angular and deep ; anterior cicatrices conflu- 

 ent, large and well impressed ; posterior cicatrices confluent, large and slightly 

 impressed; dorsal cicatrices placed in a row in and above the centre of the cavity of 

 the beaks ; cavity of the shell rather deep and wide ; cavity of the beaks rather 

 shallow and rounded ; nacre bluish-white and iridescent. 



Soft Parts. ■^—T\iQs,Q; were not in alcohol, and were so dried as to present no per- 

 fectly developed charactei's, except that the anal opening was without any papillae. 

 The branchial opening is large, and has large colored papillae. The palpi seem to be 

 large and subtriangular. No ova or embryos were found in the specimens sent to 

 me by Mr. Wheatley. The mantle is very thin, with a broad margin. 



Remarks. — Among a number of interesting shells from Asia I am indebted for this 

 to Mr. Wheatley, who is untiring in efforts to procure from Western Asia the fresh- 

 water shells of that little known country to science. This species has a resemblance 

 to M. Wheatleyi (nobis), but that species is not arcuate, and the nacre is brighter and 

 more disposed to be golden, nor does the nacre thicken before. There is also a 

 difTerence in the color of the epidermis, the Wheatleyi being of a light straw color, and 

 having the lines of growth more distant and better defined. The Mardinen-ns has 

 very minute granulations in the cavity of the shell, which along the margin are 

 usually replaced by beautiful minute strife. Among the species described by M. 

 Bourguignat in Pe Soulcy's "Voyage Autour de la Mer Morte," that which comes 

 nearest to this species is TJnio Soulcyi, which is evidently a Monocondyloia. It differs 

 from that species in being arcuate, in having larger teeth, in the lines of growth, and 

 other minor characters. The habitat of these shells is thus described in a letter to 

 me from Mr. Wheatley; " These shells are from a stream which flows from KuUeth, 

 joins another from Lore, and together reach the Tigris north of Telshehen. KuUeth 

 is twenty-one miles north, thirty-three east from Mardin, and about fifteen or 

 eighteen miles south of the Tigris." 



