No. 109. 



183 



posterior, one large and strongly impressed, the otlicr smaller, 

 lying above and between tlie larger one and Hie liinge-line ; 

 pallial impression simple. 



1, 2, 3 : Tellinomya nasjita. 



4,5: T. dubia. 



0, 7 : T. cuneata' 



In the larger species known, the hinge-line is only slightly arcuate ; 

 while among the other species we find many variations in the curvature, 

 and it sometimes becomes distinctly angular, as in T. cimeala. In some 

 species the teeth on either side of the beak curve outwards from it, and in 

 others inwards towards the beak on both sides. The teeth are often very 

 minute immediately beneath the beaks. 



The shells of this genus vary from elliptical to ovate and subtriangular 

 forms, many of them being contracted on the posterior side ; they are 

 usually of moderate thickness, though one species is very thick and strong. 

 Some of the species have a distinctly impressed lunule. The lesser muscu- 

 lar impression is often a small pit placed directly beneath the hinge-line, 

 and between it and the large muscular impression. The beaks are usually 

 of medium size, pointed, rarely ventricose, approximate or in contact, 

 never subspiral. 



* The specimens above figured were collected at Pauquette's Rapids on the Ottawa 

 River, in beds lying at the junction of the Trenton and Black-river limestones. E.B. 



