36 CANADIAN FOSSILS. 



the posterior slope or ridge only excepted, which is convex, but not 

 at all carinate. There is a slight groove below the straight cardinal 

 border. 



The ligament fulcrum extends to full half an inch from the beak, 

 and the ligament itself (often perfectly preserved in the silex) is 

 convex, and rather conspicuous. The teeth are straight, vertical, and 

 set on a moderately broad edge ; there are about eleven or twelve on 

 each side, arranged nearly in a direct line ; the hinge-plate which 

 bears them is narrowest on the anterior side, and beneath the beak 

 much contracted in depth. (In the next species it is considerably 

 broader. 



Locality. — Allumeite Islands. A new species of Lyrodesma occurs 

 with it, distinct from L. plana of the Trenton limestone. 



C. Logani. 



Plate VIII. Figure 3. 



C. uncialis, convcxa, antice rotundalafere gibba, postice subtruncata obtusi- 

 carhiata; umbone subcentrali eminente; dentibus anticis 7, jwsticis 9 

 curvatis. 



Synonym. — Tellinomya dubia, Hall, Report Regents University, pi. c, 

 figures 4, 5 (not of Pal. New York, plate 34, vol. i.). 



An elegant species, which might, till closely examined, pass for a 

 variety of the last. It is much more convex, and almost gibbous 

 anteriorly: the posterior side more decidedly contracted and sub- 

 carinate above. The beak is rounded, but elevated and placed 

 centrally, or rather nearer to the subtruncate posterior end than the 

 other. There is no lunette. 



The teeth are placed on a gently curved hinge-plate, which is not 

 indented by so prominent a ligament fulcrum as in the other species. 

 Those on the anterior side are straight, prominent, and simple ; the 

 posterior ones are bent towards the centre, and those beneath the 

 beak crowded, no space being left between the anterior and posterior 

 sets. 



The anterior shews that the adductor impressions were not so deep 

 as in the next described and smaller species. 



As the larger fossil above described cannot bear the name I had 

 originally proposed, and as the name Ctenodonta Logani has appeared 



