INVERTEBRATE PALAEONTOLOGY. 185 



the anterior one being a little deeper and narrower than the other ; pallial 



sinus trigonal, ascending, rather deep, or slightly longer than wide. 



Length of one of the largest specimens seen, 1 47 inches ; height, 1.25 

 inches; convexity, 0.85 inch. Smaller specimens proportionally slightly 

 higher and more compressed. 



By breaking away portions of the valves about the beaks of several 

 specimens of this species I have succeeded in making out the details of the 

 hinge quite clearly. In the left valve, the anterior lateral or lunular tooth is 

 not connected with the anterior cardinal, but distinct, moderately prominent, 

 rather long, and ranges parallel to the margin above. Of the anterior two 

 cardinal teeth (which are approximate, and at the apex even connected), the 

 anterior one is very narrow, or laterally compressed, and ranges vertically 

 under the point of the beak, while the other is thicker and more oblique. 

 Behind the latter, there is a still more oblique, rather wide pit for the recep- 

 tion of the posterior and largest tooth of the other valve; while immediately 

 behind this pit is the posterior cardinal, which is long, slender, and oblique. 

 In the right valve, the pit for the reception of the lunular tooth is well defined, 

 and just behind this the anterior cardinal is seen to be very narrow, and 

 ranging nearly vertically, so near the larger, very slightly oblique middle 

 tooth, as merely to leave a narrow, slit-like pit for the reception of the com- 

 pressed anterior cardinal of the other valve. Just behind the middle cardinal 

 of this valve, the rather large, more oblique pit for the reception of the 

 stronger middle tooth of the left valve occurs, and behind this pit the rather 

 strong, oblique, longer posterior cardinal is seen, with a narrow, elongated, 

 oblique furrow behind it for the reception of the oblique posterior cardinal of 

 the other valve. Behind the cardinal teeth, the hinge-margin is strong for 

 some distance back, and somewhat thickened in one or both valves, so as to 

 form a kind of posterior lateral tooth, quite remote from the cardinals. 



The foregoing description is made out from large, fully-developed speci- 

 mens, which I at one time thought might represent a more developed form 

 of our species C. Deweyi ; but a more careful comparison shows that they not 

 only differ from that species in their larger size and thicker shell, but in hav- 

 ing a more excavated lunule, a longer ligament, and a kind of excavated, 

 narrow escutcheon. My present opinion is that these shells represent only a 

 more robust growth of our species C. Nebrmcensis, which was founded upon 

 24 it 



