FISHES OF THE CARBONIFEROUS SYSTEM. 91 
Formation and locality: Chemung group; Warren, Pa. Collected by 
Mr. F. A. Randall. 
DirrErRuUS (CTENODUS) MINUTUS, Nn. Sp. 
Plate XXVII, Fig. 26. 
Teeth small, two to five lines in diameter; ovoid or oblong in outline, 
vently arched, inner angle of crown smooth; two-thirds of the outer surface 
occupied by five to seven divergent tuberculated ridges. 
These little teeth might be supposed to be simply those of the young 
of some of the larger species with which they are associated, but their form 
and markings are such as suffice at once to distinguish them. Aside from 
their small size they differ from the teeth of D. Nelsoni, which they most 
resemble, in having the ridges strongly tuberculated, while in the larger 
species they are without tubercles. D. flabelliformis is much flatter, with a 
larger number of ridges, and these more obtusely tuberculated, while in 
D. levis the teeth are of quite different form, and the ridges are without 
tubercles. Hence we are compelied to regard these as the teeth of a small 
but well marked species of Dipterus, and one which resembles more than its 
associates the teeth of the Carboniferous genus Ctenodus, in many of which 
the ridges are almost equal in size and divergence, and are composed of 
closely set tubercles that terminate above in sharp points deflected outward. 
To these the teeth before us are quite similar, and illustrate what has been 
said in the notes on the genus, of the impossibility of drawing any sharp 
line of demarkation between Dipterus and Ctenodus. 
Formation and locality: Chemung conglomerate; Warren, Pa. Col- 
lected by Mr. F. A. Randall. 
SPHENOPHORUS, nov. gen. 
Of the fish to which I have given this name only a clavicle is yet 
known to me; this is a flattened bone, six inches or more in length by 
one and a half inches in width at the middle, narrowing to either end; the 
anterior margin strongly reflexed; the exterior surface is marked by many 
rows of relatively large arrowhead-like tubercles, closely set one behind 
the other, the points directed forward. 
