LAMKU.II'.KAM II1ATA 



convex. >traight liehiml the lieak-. anterior eml -hort,-8eniicirciil.u ; \entral margin 

 gently convex; r eml ;i little narrow ei than the anterior and morr .sharply 



roumle-l. Surface with o|, M -inv concentric lint-: -loping ra|ii.lly .it the cardinal 

 margin, i.ut very gently to the ends and ventral edge. Hinge plate of moderate 

 strength, bent a little beneath the beak and with a thickening on the lower side in 

 front <>f same. Posterior to the beak the plate is long, straight and hears twenty or 

 more Miiall teeth, while on the anterior part only nine are to be counted. In the 

 vicinity of the U'.ik the teeth, especially those on the posterior side, are very small. 

 an. I us they are all set at right angles to the hinge plate, the continuity of the series 

 i- interrupted where the two series come together. The interruption is easily over- 

 .'<!, because of the slight beii'l in the hinge plate. Anterior muscular impression 

 deep, -it u. it. ..I immediately beneath the end of the hinge. Its posterior side is defined 

 by a strong vertical thickening of the shell, in the upper part of which the scar of a 

 -mall pedal muscle is to be observed. Posterior scar distinct, but less sharply 

 impressed than the anterior, situated at the end of the hinge just within the thin 

 post-cardinal Border of the shell. 



The characters of the hinge and the deep muscular impressions show that tin- 

 species is related to ('. planodorx<itn, with which it is also associated in the shales. 

 There is.- however, room for several intermediate species, the form being much more 

 elongate, the back not flattened, the posterior end rounded instead of subacute, and 

 the hinge much less bent. In C. subnasuta the shape is somewhat similar, but the 

 hinge is different, the muscular impression not nearly so distinct, the beaks larger 

 ami situated farther from the anterior end. while the anterior half is relatively 

 higher. 



formation and locality. Middle thin! of th>- Trvnton shales, Ooortbu.- munly, MIooMoU; SMO- 

 1 with C planadortata, C. romjtrtun, C. toeialif and C. co 



C. logani section. 



t'TKNODONTA LOOAIU Salt- 

 TI.ATF Mil FI08. ; 



T.lli H ,>my,i ,lui- -i II \ i Tenth Ann. Rep. Beg. I ni \ "i ; 183, Kg* 4 aod 5. (Not 



T. dubia Hall. 1847, F.I 



t,,nta ;.v > ALTER. 1869. Canadian Organic He mains. Dec. I. p. 36. (Not C. logani Sailer, 

 1661, Rep. BriU Aacoc., p. 93, which proved to be the same a* 

 Tellinomga namta Hall, IMT.i 



Shell of the medium M/-. rather elongate, sabovate, strong! x, very gib- 



bous in the umbonal region, with the strongly incn ik- turned slightly forward 



and -ituated near the midlength; posterior en<l a little the narrower. roun<le<l. l-ut 

 not quite uniformly, the lower part neinj: usually a tritle prominent: kisal margin 

 y arcuate, the po.t-rior half somewhat less convex than the ai.' anterior 



