DESCRIPTION OF FIFTY-TWO SPECIES OF UNIONID^. 27 



Shell smooth, round, very much inflated, subglobose, very inequilateral, rounded 

 before and behind; substance of the shell thick, much thicker before; beaks raised, 

 swollen, somewhat retuse ; ligament rather large and light brown ; epidermis yel- 

 lowish olive, with rather indistinct rays over the whole disk, and with rather dis- 

 tant marks of growth ; umbonial slope rounded ; posterior slope elliptical, with 

 two indistinct impressed lines on each valve from the beak to the margin; cardi- 

 nal teeth rather small, subconical, double in the left and treble in the right valve ; 

 lateral teeth long, thick and nearly straight; anterior cicatrices distinct, rather 

 small and deeply impressed ; posterior cicatrices confluent, rather large and well 

 impressed ; dorsal cicatrices placed nearly in the centre of the cavity of the beaks; 

 cavity of the shell deep and rounded ; cavity of the beaks shallow and obtusely 

 angular ; nacre beautifully white and iridescent. 



Remarks. — A single specimen only was brought by Mr. Peale from Kansas. 

 It is always to be regretted that a description should be made from a single 

 specimen, as the species of this genus often vary exceedingly. In outline it is 

 perhaps nearest to ebenus (nobis), but it has not the high retuse beaks of that spe- 

 cies, nor its dark margin or peculiar party color of the young shell. In the epi- 

 dermis it is totally different. It is not quite so round as circulus (nobis), and 

 differing so much in the epidermis, cannot be confounded with that species. In 

 the color of the epidermis and indistinct rays it is allied to ellipsis (nobis), but it 

 is not so oblique. The beaks are nearly perfect, and show indistinctly very minute 

 undulations at the tips. I dedicate the species to Mr. Peale, who presented it to 

 the Academy with many other species from the distant habitat of Kansas. 



Unio acuens. pi. 8, fig. 24. 



Testa Isevi, triangulari, compressa, valde infequilaterali, antice rotundata, postice subbiangulata ; val- 

 vulis crassiuscalis, antice crassioribus ; natibus prominentibus ; epidermide luteola, radiis inter- 

 ruptis ; dentibus cardinalibus subcrassis, subcompressis crenulatisque ; lateralibus subcrassis, 

 brevis subrectisque ; margarita alba et iridescente. 



Shell smooth, triangular, compressed, very inequilateral, rounded before and sub- 

 biangular behind ; valves somewhat thick, thicker before ; beaks prominent ; epi- 

 dermis yellowish, with interrupted rays ; cardinal teeth somewhat thick, somewhat 

 compressed and crenulate; lateral teeth somewhat thick, short and nearly straight; 

 nacre white and iridescent. 



Proc. Acad. Nat. ScL, 1811, p. 3 90. 



Hah. — Holston Eiver, near Concord, East Tennessee, Miss A. E. Law. 



My cabinet and cabinet of Dr. Lewis. 



