PISIDIUM. 23 



peculiarly appropriate to tlie 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 i)eaks 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. Oval. 



3. P. pusii/lum*, Gmelin. 



Tellina pusilla, G-inelin, Syst. Nat. p. 3231 . P. 'pusillum, F. & H. ii. 

 p. 123, pi. xxxvii. f. 10, and (animal) pi. O. 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 httle 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 : beaks not prominent, but blunt : liga- 

 ment short and inconspicuous: inside greyish-white, vrith 



* Little. 



