Cope.] Yd A [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 

 little elevated. The longer ones project heyond 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 this species is found 

 is the smallest yet obtained from the formation. Length, .007 ; width, 

 .003 ; depth at inner crest, .003. 



Two specimens were found by Wm. Gurley, in Vermilion Co., Illinois, 

 in the 'Glepsydrops shale. 



I have referred two species from this formation to the genus Geratodus, 

 under the names of G. vinslovii and G. paucicristatus. While the form of 

 these teeth is that of the genus named, the structure of the superficial layer 

 differs in- wanting the punctse which are characteristic of Geratodus, but is, 

 on the contrary, uniformly dense, although frequently irregular. I there- 

 fore refer the two species above mentioned to anotner and allied genus, 

 under the name Ptyonodus, with G. vinslovii as type. 



Orthacanthus qjtadriseriatus, Cope, sp. nov. 



Represented by an incomplete radial spine. With it occur several frag- 

 mentary spines which resemble very closely one belonging to 0. gracilis, 

 Newb. (Geolog. Survey of Ohio, PI. lxix, fig. 7), and which only differ 

 in having the denticles shorter. As teeth of a Diplodus near to or identical 

 with J), 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. 



Arch^eobelus 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 Gurley. 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 



