8 SPHJERIIDM. 



Shell somewhat triangular, rather swollen, solid, glossy, with 

 deep concentric grooves, greyish horn-colour ; epider-mis thick- 

 ish ; ^;^/<?;7'^r J-/^^ abruptly truncate ; posterior side considerably 

 produced (lengthened) and sloping downwards towards the 

 lower margin ; lower margin obliquely curved ; ligament short, 

 visible outside ; itiside bluish-grey, pearly ; teeth same as in 

 Sphcerium, the lateral ones strong ; scars deepish. 



Inhabits slow running rivers, lakes, ponds, and 

 canals throughout Great Britain. 



2. P. fontina'le,* Draparnaud. Pl. I. 



Body whitish or greyish, slightly transparent ; foot rather long, 

 somewhat pointed ; mantle bordered with grey ; siphon some- 

 what conical, obliquely truncate at its extremity, orifice large 

 and flexible. 



Shell somewhat triangular, swollen, thin, shining, greyish, 

 with fine, irregular concentric striae ; epidermis very thin ; 

 anterior side abruptly truncate ; posterior side rounded and 

 gradually sloping downwards ; beaks prominent and somewhat 

 pointed ; ligament short, indistinct ; inside whitish, pearly ; 

 hinge short, thick ; teeth as in last species ; scars deepish. 



Inhabits sluggish rivers, canals, ponds, &c., through- 

 out Great Britain. It is considerably smaller than 

 the last species, and also differs from it in being 

 thinner, and in having the posterior margin somewhat 

 less produced, the beaks more prominent, and the 

 ligament less distinct. 



Var. I. Henslowana. — Each valve with a plate-like appendage 

 near the beaks. Occurs in many of the northern, eastern, home, 

 and south-western counties of England, as well as in South 

 Wales and Cork, B.C. Barnsley Canal near Wakefield (J. 

 Hebden), near Birmingham (G. Sherriff Tye), J.C. 



Var. 2. pidchella. — Shell more glossy, strongly and regularly 

 grooved ; beaks less acute. More common than the last variety, 



B.C. . 



* Tnhabitinrj fountains. 



