FISHES OF THE CARBONIFEROUS SYSTEM. 87 
selves, but are symmetrical with those on the other side, the lateral ridges 
being shortest and bearing several tubercles, while those which border the 
central furrow have but a single tubercle at the extremity of each. On 
both sides of the central boss the crown of the tooth is worn in a shallow, 
rounded depression by the opposing teeth of the lower jaw. The posterior’ 
margin of the crown is nearly straight, and is slightly crenulated at the 
center. It is bordered laterally by a sloping surface, which extends down- 
ward and backward about four lines and expands to form low, wing- 
like projections. This portion of the tooth was doubtless covered with 
integument. 
Formation and locality: Upper Chemung rocks; northern Pennsylvania. 
Collected by Mr. Andrew Sherwood. 
Genus DIPTERUS, Ag. 
On the following pages a number of species of the fan-shaped palate 
teeth so common in the Devonian and Carboniferous rocks of the Old 
World are described as species of Dipterus. Until recently the group of 
fishes which they represent was unknown on this continent, and even when 
the first volume of the Paleeontology of Ohio was published their paucity 
was remarked upon as strange and inexplicable. . A few years, however 
have made quite a change in the aspect of the problem, as a large number 
of teeth which clearly belong to the group of fishes which Pander called 
Ctenodipterines have been obtained from rocks of several different systems; 
for example, from the Jurassic of Colorado, the Permo-Carboniferous of 
Indiana, the Carboniferous of Ohio, and from the Chemung and Catskill of 
Pennsylvania and New York. All these have the same general form and 
structure, and are so much alike that it is difficult if not impossible to sepa- 
rate them into generic groups. The teeth from the higher horizons are 
without tubercles on the ridges, while in the Carboniferous and Devonian 
they are often conspicuously marked in this manner; but there are smooth 
species in the older as well as in the newer rocks, and they cannot be 
grouped by any geological lines. By convention those found in the Juras- 
sic, Triassic, and Permian have been called Ceratodus, those in the Carbon- 
iferous Ctenodus, and those from the Devonian Dipterus. 'The experienced 
