440 



Silurian and Devonian Fossils of Canada. 



impression sub-circular, superficial and situated just beneath the 

 posterior extremity of the hinge line. 



The specimen is deeply imbedded in a coral [Monticulipora 

 petropolitana), and only exhibits the edges and inside of the shell. 

 From the great thickness of the shell, casts of the interior must 

 bear very little resemblance to a perfect specimen. The form is 

 very like that of Vanuxemia inconstans, but the characters of the 

 interior leave no doubt as to its distinctness. 



Locality and Formation. — Bayfield Sound, Lake Huron a sin- 

 gle loose specimen ; Lower Silurian ; appears to be of the Hudson 

 River Group. 



Collector. — A. Murray. 



Genus Matheria (Billings). 



Generic Characters. — Transverse ; equivalve ; inequilateral ; 

 beaks near the anterior end ; dorsal and ventral margins sub- 

 parallel; two small obtuse cardinal teeth in the left valve, and 

 one in the right ; no lateral teeth; two muscular impressions' 

 ligament external. 



This genus is dedicated to Mather, one of the Geologists of 

 the New York Survey. 



Matheria tener. 



Fig. 18. 



Figure 18. A, dorsal view of Matheria tener ; B, interior of right valve ; 

 C, exterior of left valve ; D, interior of left valve. 



Description. — Small, oblong, depressed; dorsal and ventral 

 margins nearly straight and parallel ; upper half of posterior 

 extremity obliquely truncate ; lower half rounded ; anterior 

 extremity sub-truncate from the beaks nearly to the anterior ven- 

 tral angle, which is rounded, and projects slightly beyond the 

 umbones. From the beaks to the anterior ventral ansle extends 



