28 NEW UNIONID/E OF THE 



Branchial opening small, with rather small brown papillae. Anal opening large, 



with very small brownish papillae. Sup>er-anal opening . Color of the mass 



whitish.* 



Bemarhs. — This belongs to the group of which clavus Lam. may be considered the 

 type, and to which decisus (nobis) and paiulus (nobis) belong. It is most nearly 

 allied to decisus, and to this species I referred the first specimens I received ; but on 

 getting more from different habitats I found the characters so persistent that I do not 

 hesitate to assign a new name to it. It differs from decisus in being usually larger 

 at the umbones, and in being more compressed and dilate on the posterior portion, 

 also in having, with rare exceptions, well marked, green, transverse bands along the 

 lines of growth, which the decisu/i has not, but on the contrary is obscurely I'ayed. I 

 owe to different friends a fine suite of this species, young and old, but not one with 

 perfect beaks, so that the character of the undulations might be noted : they are 

 probably few and large. The youngest of those before me is not one-fifth the size of 

 largest. All the youngest have transverse bands over the whole disk — the older ones 

 do not possess it generally from the middle to the margin. A single old specimen 

 with much eroded beaks presents no band. Some of the specimens have the bands 

 much closer than in the figure ; one of them having four where this has two. The 

 direction of the cardinal teeth is very remarkable, being in a line parallel to the 

 lateral teeth. The size of the cardinal teeth differs, the young having them smaller 

 in proportion to the older. 



Unio Downiei. Pi 25, fig. 91. 



Testa laevi, elliptica, inflata, post-ice subtriangulata, inajquilaterali ; valvulis crassis ; natibus prominulis ; 

 epidermide tenebroso-fusca, striata ; dentibus cardinalibus subgrandibus, crenulatis, striatis, in utroque 

 valvule subduplicibus ; lateralibiis sublongis, crassis subcurvisque ; margarita purpurea et iridescente. 



Shell smooth, inflated, somewhat biangular behind, inequilateral ; valves thick ; 

 beaks somewhat prominent ; epidermis dark brown, striate ; cardinal teeth somewhat 

 large, crenulate, striate and double in both valves ; lateral teeth rather long, thick and 

 somewhat curved ; nacre purple and iridescent. 

 Proe. Acad. Nat. Sci., 1858, p. 16G. 



^a6.— Buck Lake, a bayou of Satilla River, Wayne County, Georgia. T. C. Dowuie 

 and J. Postell. 



My cabinet and cabinets of Mr. Downie and Mr. Postell. 

 Diara. 1-5, Length 1-9, Breadth 3-3 inches. 



Shell smooth, inflated, somewhat biangular behind and regularly rounded before, 

 inequilateral ; substance of the shell thick, somewhat thickened before ; beaks 

 somewhat prominent ; ligament rather short, thick and dark brown; epidermis dark 



*Tlie specimen was in a very bad cuudition, therefore some of the characters could not be made out 

 satisfactorily, and some not at all. 



