582 THE AMERICAN NATURALIST. 
tion of the whorls of Helicoprion. As for Helodus coxanus, 
cited by the Russian director, it may be remarked that, after a 
study of the type specimen (now in the keeping of the U. S. 
National Museum) in connection with a large series of dental 
plates of Cochliodus latus from the same horizon, the reviewer is 
satisfied that they were associated in one and the same mouth. 
H. coxanus is, accordingly, but another name for one of the 
several arched series of knob-like teeth situated in advance of 
the large pair of dental plates in the upper and lower jaws of 
Cochliodus latus. 
A very curious case of coiling among cochliodonts which has 
not been previously reported occurs in Sandalodus levissimus, 
which accompanies Cochliodus latus in the Keokuk limestone 
of Iowa and Illinois. The initial portion of the large posterior 
dental plate is wound upon itself one and a half times before 
expanding into the functional grinding surface characterizing 
the adult, and in De/todus undulatus from the Burlington lime- 
stone a like condition obtains on a somewhat smaller scale. 
These instances deserve notice, when we consider the variety 
of evidence it is necessary to take into account before pass- 
ing judgment on the extremely problematical nature of the 
Edestide. In Fig. 1 is shown one of the most perfect exam- 
ples of Sandalodus ever discovered, and its bearing on the 
present subject will be evident from inspection. 
