536 THE PALEONTOLOGY OF MINNESOTA. 
(Cyrtodonta subovata. 
The above is a fair statement of the case as I found it when I began the 
present work. Had my studies shown what both Billings and Hall conceded to be 
the case, that Conrad’s sketch of the hinge of Cypricardites was identical with that 
of Cyrtodonta and Palwarca, 1 would most surely have sided with Hall and adopted 
the oldest name. But here was the rub. Comparisons with the hinges of numerous 
species of this family of shells have demonstrated beyond question that Conrad’s 
figure and description of the hinge of Cypricardites does not correspond exactly 
with that of any true Cyrtodonta or Vanuxemia known. He represents the cardinal 
teeth as diverging from the beak much as in a Lyrodesma and says that the anterior 
one is the “largest and most prominent”. Neither of these conditions is ever 
present in Crytodonta. On the contrary the teeth are subparallel, and to be called 
horizontal rather than radial, while the anterior one, if any can be so called, is the 
smaller. Nor have I seen any Cyrtodonta with five cardinal teeth, the usual 
number being three; two is not uncommon, but four is very rare. 
‘We are now confronted with the question, did Conrad correctly describe and 
illustrate the hinge of his genus? This question can be determined only by a study 
of the type of the genus. But here again we meet with trouble for of the sixteen 
species originally referred to the genus only one, his C. curtus remains, the others 
having proved generically distinct, being now referred to other genera. The genus 
must then, if it stands at all, be based upon C.curtus. I do not know whether the 
hinge drawn by Conrad represents that of this species or not. For the present we 
must assume that it does, and further, until we know the contrary, it must be 
accepted as correct. From this standpoint then it is evident that Cyrtodonta and 
Cypricardites are not synomymous, and that both may stand for the present. I 
would suggest that, however the question may be eventually terminated, Cypricar- 
dites may for a long time to come serve as a convenient temporary receptacle for 
those species which because they are insufficiently known cannot be definitely 
placed into other genera. 
CyRTODONTA SUBOVATA, %. SD. 
PLATE XXXIX, FIGS. 28, 29, 31-33, ? 30 and ? 45. 
Shell somewhat obliquely ovate, narrowest anteriorly. Dorsal margin short, 
less than half the length of the shell posterior to the beaks merging gradually into 
the uniformly rounded posterior margin, hase gently convex, anterior end short and 
rather narrowly rounded; outline distinctly concave between the anterior extremity 
and the projecting umbones. Beaks incurved, umbones prominently rounded, 
inconspicuous. A slight flattening of the surface between the umbonal ridge and 
