50 PALEOZOIC FISHES OF NORTH AMERICA. 
outline, from which the sides converge upward to an irregularly flattened 
and roughened crown, that rises at the anterior extremity into a pointed 
prominence; base excavated; crown thick and strong; upper surface show- 
ing attrition from use. 
In the teeth described above we have a form of which a number of 
examples have been taken from the Corniferous limestone. None of these, 
however, are sufficiently complete to enable us to give all desirable details 
of their normal outlines and structure. So far as we can judge from this 
material, the original form of these teeth was not unlike that of the one I 
have described under the name of Rhynchodus secans, but they were evi- 
dently much thicker and stronger, and were fitted for crushing rather than 
for cutting. For the reasons already given I have been led to group these 
with the other teeth now described under the same generic title, and to 
regard them as the remains of fishes having more affinity with Chimera and 
Callorhynchus than with any others now living. 
Probably the accumulation of more material will enable future paleon- 
tologists to determine more accurately the relations of this group of fishes 
with each other and with our living fauna; and it is possible that their 
researches will modify in some degree the views now advanced. I have 
thought, however, that the publication of figures and descriptions of this 
singular group of fossils would at least serve a useful purpose in stimulating 
collections and researches by which their structure and relations would be 
more fully ascertained. 
Formation and locality: Corniferous limestone; Sandusky, Delaware, 
and Kelley’s Island, Ohio. 
RuyncHopus Excavatus, Newb. 
Plate XXIX, Figs. 1, 1°. 
Rk. excavatus, N.; Geol. Survey Wisconsin, vol. 2, 1877, p. 396. 
Tooth small; size when entire perhaps two and a half inches long by 
one and a quarter deep; the crown alone preserved. Of this the external 
surface is marked vertically with vermicular furrows; superior margin sin- 
uous, terminating anteriorly in a prominent point; the superior surface 
irregularly excavated and roughened, showing two elevations or tubercles, 
