Cope.] 192 [Nov. 2, 
crest which is convex inwards. The crests are straight, elevated and 
acute ; each one supports two or three denticles, which are rectangular and 
littie elevated. The longer ones project beyond the general outline ; the 
shorter ones are less prominent at the extremities; all are obtuse in the 
vertical direction. The superior surface is smooth. The inferior is slightly 
concave in the transverse sense. The tooth on which tlris species is found 
is the smallest yet obtained from the formation. Length, .007; width, 
.008 ; depth at inner crest, .003. 
Two specimens were found by Wm. Gurley, in Vermilion Co., [linois, 
in the Clepsydrops shale. 
T have referred two species from this formation to the genus Veratodus, 
under the names of C. vinslovid and CO. paucicristatus. While the form of 
these teeth is that of the genus named, the structure of the superficial layer 
differs in wanting the puncte which are characteristic of Ceratodus, but is, 
on the contrary, uniformly dense, although frequently irregular. I there- 
fore refer the two species above mentioned to another and allied genus, 
under the name Ptyonodus, with C. vinslovid as type. 
ORTHACANTHUS QUADRISERIATUS, Cope, sp. nov. 
Represented by an incomplete radial spine. With it occur several frag- 
mentary spines which resemble very closely one belonging to O. gracilis, 
Newb. (Geolog. Survey of Ohio, Pl. lxix, fig. 7), and which only differ 
in having the denticles shorter. As teeth of a Diplodus near to or identical 
with D. compressus are common in the shale, the two may belong to the 
same fish. Dr. Newberry has already suggested that Orthacanthus and 
Diplodus are identical. 
The 0. quadriseriatus is quite different from the other species. The 
spine is wider than deep, and the series of denticles are widely separated. 
The surface between them is gently convex and smooth. The anterior 
face is strongly convex and presents at each side two shallow furrows. 
The external groove is divided by a series of thin longitudinal denticles 
which are smaller than those of the principal row, and which are some- 
times somewhat confluent at the base. The principle denticles are closely 
placed, stout, acute, and recurved. Transverse diameter of shaft .0035 ; 
antero-posterior diameter .0025. The portion of the shaft preserved is 
straight. 
ARCHA®OBELUS VELLICATUS, gen. et sp. nov. 
‘“Species No. 4,’’ Cope, Proceed. Amer. Philos. Soc. 1877, p. 55. 
Several other specimens of the body described as above have been ob- 
tained by Messrs Winslow and Guriey. In every instance it is a tooth-like 
process attached to a solid base by anchylosis in the manner of the teeth 
of fishes. From the appearance it presents I am led to suppose that it is 
the only one of its series, and there are none of the numerous teeth of the 
collections which can be associated with it. I therefore distinguish the 
genus by a name and the following diagnosis. 
The form is conical, and the surface is not grooved nor furnished with 
