197 



Unio ater, Lea. Trans. Am. Phil. Soc, vol. 3, pi. 7, New iSeries. 



Obs. I received several specimens of this shell from Mr. Bara- 

 bino, who obtained them from Bayou Teche, Parish of St. Mary, 

 Louisiana. It seem to be intermediate, and almost connected by 

 means of varieties, to U. cariosus, nob., and ventricosus, Barnes ; 

 like those species it has the posterior side prominent and very 

 short, the anterior margin often truncate and the primaiy teeth 

 often double in both valves ; but, however close this alliance may 

 be, it can be distinguished by its somewhat different habit. It is 

 differently colored, less cylindrical than cariosus, and proportion- 

 ally longer and more cylindrical than ventricosus. 



In the young state the ligament margin appears to be coalite, 

 and that of the older shell retains this union on its anterior portion . 



The name afcr is preoccupied by Nilsson for a very distinct 

 species. PI. 43. 



Crepidula. — Shell free, univalve, irregular, ovate or oblong, 

 convex, somewhat patelliform, with an epidermis ; spire very short 

 or obsolete, apex obvious, obliquely inclined, towards the margin : 

 within horizontally divided about half the length by a diaphragm ; 

 muscular impression lunate. 



Animal more or less depressed, oval, curved in the posterior 

 part ; mantle very thin, without marginal tentacula ; foot not 

 thick, small and rounded ; body each side of the head auriculated ; 

 head emarginate before ; tentacula two, subcylindric, or subconic, 

 slightly contractile, with the eyes near their exterior base ; mouth 

 in the emargination, without teeth; branchial cavity very large, 

 situated on the anterior part of the back, containing a fascicle of 

 long branchial filaments, which extend forward, and at tip float on 

 the right side of the neck ; anus on the right side. 



Obs. These are marine shells attaching themselves to various 

 objects. At least many of the species have no locomotion, passing 

 their whole life in one spot, and being moulded upon the surface 

 of their resting place, exhibit its curvature and inequalities. 



Lamarck separated the species from the Linneau Patellse, form- 

 ing a very natural and very distinct group. For although it ex- 

 hibits a slight similarity to Septaria, Feruss., yet it is readily 

 distinguished from that shell, which has not a proper diaphragm, 

 the labium being only a little prominent and acute ; it is also a 

 fresh water, operculated shell, allied to Neritina. 



