Silurian and Devonian Fossils of Canada. 439 



is broadly rounded ; dorsal margin slightly and uniformly convex 

 from the beaks to the posterior angle ; anterior extremity repre- 

 sented by a very small projection beneath the beaks ; ventral side 

 regularly rounded, except a short pace near the beaks, which is 

 sometimes concave and partly occupied by the small projection of 

 the anterior extremity. Three strong curving anterior teeth ; two 

 posterior lateral teeth ; shell very thick towards the anterior end ; 

 a small area between the beaks ; the anterior muscular impression 

 is apparently excavated in the edge of the very thick shell. Sur- 

 face with a few more or less strongly marked concentric furrows 

 of growth. The beaks are short, rounded, and closely incurved. 



The proportional length and breadth varies. The specimens are 

 usually an inch and a half in length from the beaks to the poste- 

 rior extremity, the greatest width from the dorsal to the ventral 

 side being an inch and three or four lines. There is a small va- 

 riety, scarcely an inch in length, and more obtuse at the anterior 

 end, than the specimen figured ; it is also more ventricose. 



Locality and Formation. — Fourth Chute of ibe Bonne-chere, La 

 Petite Chaudiere Rapids near the city of Ottawa, and numerous 

 localities in the valley of the Ottawa, associated with fossils of the 

 Black River and Trenton formations. 



Collectors. — Sir W. E. Logan, E. Billings, J. Richardson. 



Vanuxemia Bayfieldii (Billings). 



Fig. IT. 

 Figure IT. Interior of the left valve of V. Bayfieldii.. 



Description. — Very ventricose; ovate; the anterior extremity,, 

 including the beaks, narrowly rouuded ; the posterior end broadly 

 rounded ; shell very thick ; seven anterior teeth ; four posterior 

 teeth ; anterior muscular impression large, deep, and excavated in 

 the very much thickened edge of the shell ; posterior muscular 



