On the Genus Tellinomyu, and allied Genera. 391 



More recently the extensive collections of the Canada Geologi- 

 cal 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 meantime, 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 species 

 of Tellinomya^ closely allied to the T. nasuta of the Trenton lime- 

 stone. Mr. Woodward, in his "Treatise," places the genus 

 Ctenodonta as synonymous with Isoarca of Munster; while, 

 according to Pictet, it would be placed under the genus Nucula. 



The character of the hinge of Tcllinomya nasuta^ and of T, 

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

 a close relation to nucula^ and that it is identical with Cteno- 

 donta. 



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

 ter, large and often sub-spiral 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, equivalve, equilateral or sub- 

 equilateral, closed, smooth or marked by lines of growth ; ligament, 

 external ; hinge line, curved, sometimes sub-angular, with a conti- 

 nuous 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 posterior, one 

 large and strongly impressed, the other smaller, lying above and 



to the confusion, the same author has placed the species of Modiolopsis also 

 under the genus Lyonsia. In this reference he has been followed by one 

 American author. 



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

 some beautiful exhibitions of the hinge of Modiolopsis, which I hope to 

 have the privilege of illustrating at no distant pcM-iod. 



M. d'Orbigny places Nucula Jevata under the genus Leda, while he 

 leaves the N. donaciformis under Nucula. Both these shells belong to the 

 genus Tellinomya. 



