110 ON THE LAND AND FRESH- WATER 



This species is remarkable for its completely oval shape, which 

 renders it quite distinct from all others. Apparently rather rare 

 in Lower Canada. 



(Section B.—Spbcies with Protuberant, or Caltcclate Beaks.) 



Figure 6. 

 Sphoerium transversum, Say. sp. 



Animal white, syphonal tubes pink, foot white. 



Shell transversely oblong, elongated, sub-inequilateral, translu- 

 cent ; anterior side narrow ; anterior margin rounded, posterior 

 margin sub-truncate,basal very much curved; beaks placed somewhat 

 on the anterior side, large, calyculate, very much raised above the 

 outline of the shell ; striae very delicate ; epidermis greenish-yellow 

 (generally whitish in Canadian specimens), of a darker shade at 

 times in the region of the beaks ; valves slight ; interioi bluish - 

 hinge margin very nearly straight, narrow ; cardinal teeth com- 

 pressed, in the shape of the letter V reversed, and very much 

 expanded ; lateral teeth slightly elongated. 

 Long. 10-16; lat. 7-16 ; diam. 4-16 inches. 

 This large and delicate species is remarkable for its very trans- 

 verse shape and for the narrowness of the anterior extremity as 

 compared to the posterior. 



Figure 7. 

 Sphoerium securis, Prime. 



Animal pinkish ; syphons of the same colour. 



Shell rhombic-orbicular, ventricose, sub-equilateral, both sides 

 nearly of the same length ; anterior margin a little curved ; poste- 

 rior margin abrupt, forming an obtuse angle with the hinge margin • 

 basal margin much longer than the superior margin, rounded ; 



