22 SPH^RIID^. 



remarkable by some authors^ of the eave-like projection 

 appearing in the middle of young shells_, agrees with its 

 position in adult shells^ because this curious appendage 

 is never placed close to the beak. Var. 2. More com- 

 mon than the last variety^ and also inhabiting Sweden 

 and France. It deserves its name^ being a very pretty 

 object. Mr. Jenyns now considers it to be the same 

 species as his P. Henslowianum. Var. 3. Marshes and 

 pools near Swansea. It is probably the P. pallidum of 

 Gassies. Var. 4. Widely diffused in this country, and 

 also inhabiting France and Italy. The outline of some 

 specimens of this last variety is that of an equilateral 

 triangle. It is the P. australe of Philippi, and the Cyclas 

 lenticularis of Normand. 



This species is extremely variable, and has conse- 

 quently received a great number of names. Out of the 

 41 so-called species of Pisidium which have been de- 

 scribed by European conchologists, no less than 21 belong 

 to the present form. On the Continent the type is 

 generally known by Polios name of Casertanum. 



If the diagnosis, characters, and figures given by 

 Draparnaud for his Cyclas fontinalis had been more 

 carefully studied, it would, I think, have been obvious 

 that they do not apply to the Tellina pusilla of Gmelin, 

 with which this species has been generally (but with 

 doubt) allocated by so many authors. The principal 

 difference between these two species consists in the 

 former (P. fontinale) being triangular and somewhat 

 depressed, and having prominent beaks ; while the other 

 (P. pusillum) is oval and ventricose, and has obtuse 

 beaks. Draparnaud^s diagnosis is as follows : " C. testa 

 globosa, subdepressa, subina3quilaterali ; umbone sub- 

 acuto." Gmelin says his shell is " ovata, ventricosa ;^' 

 and his description of its colour as " sordide alba ^' is 



