PISIDIUM. 23 



peculiarly appropriate to the P. pusillum of modern 

 authors. C. Pfeiffer^ in 1821;, appears to have recog- 

 nized Draparnaud^s shell by the same specific name of 

 " fontinale ;'' and the only distinction which he makes 

 between this species and his own P. obtusale (which I 

 regard as a variety of P. pusillum) is that the former is 

 described " umbone subacuto", and the latter " umbone 

 obtusissimo/' 



It chiefly differs from P. amnicum in being very much 

 smaller (although the variety cinerea is nearly as large), 

 in the shell being thinner, the posterior margin much 

 less produced, the beaks being more prominent, and the 

 ligament scarcely conspicuous. The cardinal teeth are 

 also more separate, and do not diverge from a common 

 base or root as in that species and Sphcerium, 



B. Ovcd. 

 3. P. pusii/lum*, Gmelin. 



TelUna pusilla, Gmelin, Syst. Nat. p. 3231. P.fusillum, F. & H. ii. 

 p. 123, pi. xxxvii. f. 10, and (animal) pi. 0. f. 9. 



Body whitish, with occasionally a faint tinge of yellow or 

 red: tube short, subcorneal or cylindrical, truncate, orifice 

 small and its edges plain : foot longer than the shell, narrow 

 and slender: mantle bordered with reddish-grey. 



Shell oval, compressed but swollen, thin, not so glossy as 

 in the other species, finely but irregularly striate concentri- 

 cally, a few of the striae being larger than the others and de- 

 noting the successive stages of growth, yellowish-white or 

 cinereous : epidermis very thin : anterior side rounded : poste- 

 rior side also rounded, and sloping very gradually below ; this 

 side is very little more produced than the other, which makes 

 the contour of the shell more equilateral than in the foregoing 

 species ; both these sides are compressed, and especially above : 

 lower margin rounded : healcs not jirominent, but bkmt : liga- 

 ment short and inconspicuous: inside greyish -white, with 



* Little. 



