160 Mr. R. J. L. Guppy on a new Freshwater Bivalve. 



bodies into their substance. And the siUceous spicules of Paly- 

 thoafatua upon Hyalonema are evidently foreign bodies of this 

 sort, since, as I have described, they occur mixed with sand, 

 shells of Polythalamia, and other structures. 



I have still a word to say upon nomenclature. Dr. Bower- 

 bank names the sponge Hyalonema mirabilis. Of course there 

 is nothing to object to in this name; but Dr. Gray had already 

 (1835) named the same structure Hyalonema Sieboldi. The 

 first specimens were sent to Europe, so far as we know, by the 

 celebrated Japanese traveller Von Siebold. This name is there- 

 fore also certainly quite suitable ; and as it has the priority, I 

 think it would be well to retain it. From my observations there 

 does not appear to be the least reason for the establishment of 

 two distinct species. 



Bonn, January 1867. 



XXVII. — Description of a new Freshwater Bivalve found in Tri- 

 nidad. By R. J. Lechmere Guppy, Esq., F.G.S. 



Cyclas punctifera, Guppy. 



Shell somewhat subquadrately oval, thin, diaphanous, close, 

 finely striate concentrically, whitish horny, or 

 slightly tinted with fuscous patches near the 

 umbones, and covered with numerous granular 

 points, which are finer and more crowded on 

 the umbones, where the concentric striation 

 is less evident; anteriorly rather short and 

 subangulate, posteriorly a little truncate ; hinge 

 with well- developed lateral teeth in both valves, 

 5^ ; cardinal teeth §, small. 



This curious little shell varies somewhat, and specimens are 

 sometimes more oval and compressed than the one figured. 

 Occasionally they are higher and shorter, with a steeper poste- 

 rior slope. The granular points are more easily seen in dead 

 shells, which are opaque. In living examples they seem, under 

 a strong lens, to bear short hairs. The length of a large exam- 

 ple is 4 millimetres, height 3^ milhms., thickness 2\ miUims. 

 Of an average example the length is 3 millims., height 2| mil- 

 linis., thickness 2 millims. 



Among species of the genus Cyclas the shell now described 

 would appear to resemble most C. aryentina, D'Orb., and C. ca- 

 lyculataj Drap. It is usually more equilateral than either of 

 those species. The epidermis is thin and colourless, so that the 

 striate gills may be seen through the shell. The umbones are 

 not so prominent as those of C. calyculata, but they are occa- 



