DESCRIPTION OF FIFTY-TWO SPECIES OF TJNIONIDJE. 25 



Hah.— Mexico, C. M. Wheatley. 

 Diara. -T, Length 1-3, Breadth 1-8 inch. 



Shell winged, smooth, obovate, inflated, very inequilateral ; substance of the 

 shell exceedingly thin; beaks a little prominent, at the tips very minutely undulate 

 and pointed; ligament rather long, dark brown and nearly concealed; epidermis 

 olive color or brownish, polished, without rays, and with distant marks of growth ; 

 umbonial slope inflated and rounded; posterior slope elliptical, raised into awing; 

 anterior cicatrices confluent, large and very slightly impressed ; posterior cicatrix 

 confluent and very slightly impressed ; dorsal cicatrices placed across the cavity of 

 the shell and very slightly impressed; cavity of the shell deep and rounded; cavity 

 of the beaks exceedingly shallow"; nacre bluish and very iridescent. 



Remarks. — This very delicate species was kindly given to me by Mr. Wheatley, 

 who obtained it from a London dealer as coming from Mexico. The habitat, there- 

 fore, is not positively certain. It does not appear to me to be a Mexican species. 

 There are three specimens before me. The oldest one is dark brown with a pol- 

 ished epidermis, while the youngest is grqenish olive. The very delicate nacre, 

 which is translucent, has very minute striae passing from the centre of the beaks 

 to all parts of the margin. In outline it is closely allied to A. obtusa (Spix.), Tes- 

 tacea Fluv. Braziliencia, Tab. xxii. figs. 3 and 4 ; but difi"ers entirely in the thin- 

 ness of the valves, in not having rays, and in being higher in the wing. 



Unio Macnielii. pi. 8, fig. 22. 



Testa • sulcata, oblonga, valde insequilaterali, antice sub-rotunda, postice obtuse biangulata; valvulis 

 crassiusculis, antice crassioribus; natibus prominulis; epidermide fusca vel luteola, postice viridi- 

 radiata; dentibuscardinalibus parviusculis, compressis crenulatisqne; lateralibus sublongis lamel- 

 latisque ; margarita argentea at valde iridescente. 



Shell sulcate, oblong, very inequilateral, rounded before, obtusely biangular 

 behind; valves somewhat thick, thicker before; beaks slightly prominent; epider- 

 mis brownish or yellowish, with green rays posteriorly; cardinal teeth rather small, 

 compressed and crenulate ; lateral teeth rather long and lamellar ; nacre white and 

 very iridescent. 



Proc. Acad. ISTat. Sci., 1869, p. 124. 



Hab. — Eio Gigillillo, Corcuera, Nicaragua, Cen. Am., Mr. J. A. McNiel. 



My cabinet, and cabinet of the Peabody Academy Nat. Sci., Salem. 

 Diam. -7, Length 1-, Breadth 1-7 inch. 



Shell sulcate, oblong, very inequilateral, rounded before, obtusely biangular 

 behind ; substance of the shell somewhat thick, thicker before ; beaks slightly 

 prominent ; ligament rather short and light brown ; epidermis brownish, in the 



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