438 Silurian and Devonian Fossils of Canada, 



line, seven lines ; length of posterior and ventral sides, about ten 

 lines each. The diagonal carina is not straight, but has a strong 

 upward curve. 



Locality and Formation. — East point of St. Joseph's Island, 

 Lake Huron ; Trenton limestone. 



Collector. — A. Murray. 



Cyrtodoxta sigmoidea (Billings). 



Description. — Sub-rhomboidal, ventricose, a strong obtusely an- 

 gular carina extending from the closely appressed beaks -with a 

 sigmoid curve to the posterior ventral margin ; anterior end round- 

 ed, projecting a little in front of the beaks ; ventral margin longer 

 than the dorsal and moderately convex ; posterior extremity ob- 

 liquely truncate. Width one inch and a half; length from the 

 umbones to the ventral margin thirteen lines. 



Locality and Formation, — Hudson River group \ Anticos-ti. 



Collector. — J. Richardson. 



Sub-genus yanuxemia (Billings). 



Generic characters. — Ovate ; beaks terminal or sub-terminal ; 

 posterior extremity rounded ; anterior more or less acuminated ; 

 two muscular impressions ; anterior teeth variable in number,, 

 sometimes curved and striated ; posterior lateral teeth from two 

 to four. 



Vanuxemia ixconstans (Billings) 



Fig-. 15. Fig. 16. 



Figure 15. Right valve ; v, ventral margin ; a, the small anterior ear. 

 " 16. A fragment shewing the teeth obscurely; m, the muscular 

 impression. 



Description. — Ovate ; moderately convex ; beaks terminal gra- 

 dually expanding from the beaks to the posterior extremity, which 



