658 THE AMERICAN NATURALIST. (VoL. XXXVI. 
II. OBSERVATIONS ON EDESTUS AND COCHLIODUS. 
(From a letter addressed to Professor Louis Agassiz, dated Springfield, 
Illinois, June 29, 1871.) 
* MY DEAR PROFESSOR : 
* Excuse this postscript, but I met with rare success yester- 
day morning, in the finding of what appears to be the terminal 
denticle of an immature Edestus vorax [sic] Leidy. This is 

Fic. 3. — Detached segment of Edestus minor N. and W. Coal measures; Illinois. 
the second specimen known to me in which only a single den- 
ticle occurs — the other one, from a similar horizon in the 
Coal Measures, being referable to Edestus heinrichi N. and W., 
and readily distinguished from the former species by the 
stronger [development] and more erect position of the denti- 
cles. The slight depression at ‘a’ [Fig. 3] indicates the area 
occupied by the overlapping of the posterior extremity of the 
succeeding [z.c., preceding] denticle, which, however, is not 
a a developed in the present individual. 
* «I also received last evening à 
remarkably beautiful specimen of 
Cochliodus sp. from the St. Louis 
limestone. The specimen is very 
small, and presents two, or a pair, of 
the large posterior teeth in their 
relative position ; but what is particu- 
larly interesting, it shows the coarsely 
osseous [z.e cartilaginous] posterior 
prolongation of the rami, which appear to be terminated in 
articular processes much in the same manner as occurs in the 
modern Cestracion. The two nodes a, a [Fig. 4] are appar- 
ently the anterior prolongation of the rami for the support of the 

Fic. 4. — Cochliodus sancti-Indovici 
(St. J. and W.). St. Louis lime- 
stone; Alton, Ill. Enlarged. 
