212 DESCRIPTION OF 



Remarks. — This species has embarrassed me for some time, as I have had, 

 until recently, but few specimens. There is a close resemblance in the speci- 

 mens before me both to the U. obliquus, Lam., and U. trigonus, (nobis.) It 

 differs from both in being more rounded at the base, the emargination being 

 very small. It is higher in the beaks than the trigonus, and more flattened 

 there than the ohliquus. In colour it approaches more to the former. The 

 rays are less distinct than in the ohliquus, rarely reaching more than half-way 

 to the base. They vary very little in all the specimens I have examined. In 

 two specimens out of fourteen before me, the nacre in the cavity of the shell is 

 pale salmon colour. 



Unio Holstonensis. Plate 15, Fig. 27. 



Testa triangulari, solida, inflatd; valvulis crassis; natibus magnis, elevatis; epidermide tenebroso- 

 fuscd, radiata; dentibus cardinalibus subgrandibus ; lateralibus crassis brevibusque; 7nargaritd alba 

 et iridescente. 



Shell triangular, solid, inflated; valves tliick; beaks large and elevated; epidermis dark brown, radiated; 

 cardinal teeth rather large; lateral teeth thick and short; nacre white and iridescent. 



Hab. Holston River, Tenn. S. M. Edgar. 



My Cabinet and Cabinet of Mr. Edgar. 

 Diam. .8, Length 1.1, Breadth 1.5 inches. 



Shell triangular, solid, inflated ; substance of the shell very thick, thinner 

 behind; beaks elevated, large and solid; ligament short and rather thick; epi- 

 dermis dark brown with several large interrupted rays over the umbones ; car- 

 dinal teeth rather large ; lateral teeth oblique, short, thick and nearly straight ; 

 anterior cicatrices distinct ; posterior cicatrices distinct, the smaller one being 

 placed on the end of the lateral tooth; dorsal cicatrices scarcely perceptible, 

 placed on the inferior part of the cardinal tooth; cavity of the shell very shallow; 

 cavity of the beaks shallow and rounded ; nacre white and iridescent. 



Remarks. — A single specimen only of this shell was received with those 

 sent by Mr. Edgar. It is a well characterized little species. In outline it is 

 somewhat like U. trigonus, (nobis,) but is more rounded, has not so sharp a 

 carina and may be distinguished by its broad rays. 



