182 I Senate 



More recently the extensive collections of the Canada Geo- 

 logical Survey have furnished some beautiful examples, showing 

 in a most perfect manner the structure of the hinge, and the 

 muscular impressions of several species of this genus. 



In the mean time, a specimen taken to London by Sir William 

 E. Logan has been noticed as a new genus by Mr. Salter, under 

 the name of Ctenodonta. 



The shell upon which Mr. Salter founded this genus is a spe- 

 cies of Tellinomya, closely allied to the T. nasuta of the Trenton 

 limestone. Mr. WooimARD, in his "Treatise," places the Genus 

 Ctenodonta as synonymous wath Isoarca of Munster; while ac- 

 cording to PicTET, it would be placed under the Genus JVucula. 



The character of the hinge of Tellinomya nasuta, and of T. 

 dubia, represented in the accompanying figures, show^s that it 

 bears a close relation to JYucula, and that it is identical with 

 Ctejiodonta. 



The shells referable to this type have not the ventricose charac- 

 ter, large and often subspiral beaks, of Isoarca; nor is the beak 

 uniformly anterior, as in that genus. The species of Tellinomya, 

 so far as known, are never cancellated, or otherwise ornamented, 

 beyond the ordinary concentric lines of growth. 



Having had an opportunity of examining the hinge, and the 

 internal characters of at least six species, the following characters 

 are deduced therefrom : 



TELLINOMYA. 



Generic Characters. Shell equi valve, equilateral or subequilateral, 

 closed, smooth or marked by lines of growth; ligament exter- 

 nal ; hinge-line curved, sometimes subangular, with a continuous 

 series of small curved transverse teeth, which diminish from 

 the extremities to the beak, beneath which they are much 

 smaller ; muscular impressions double, two anterior and two 



list of fossils belonging to the Lower Silurian," is in a great measure indebted to 

 M. d'Orbigny ! 



I may mention here that the collections of the Canada Survey furnish some 

 beautiftil exhibitions of the hinge of 3Iodio I op sis, which I hope to have the privilege 

 of illustrating at no distant jjcriod. 



M. d'Orbigny places Nucula lerata under the Genus Leda, while he leaves the 

 N. donaciformis under Nucula. Both these shells belong to the Genus Tellinomya. 



