BUITALO SOCIETY OF NATURAL SCIENCES 169 



Stethacanthus praecursor, n. sp. 



(PL 54, figs. I, la, 2) 



E 1908 Cotypes. — Two nearly complete spines. 



(i) The more perfect specimen of the two; length, 82 mm. 

 (PI. 54, fig. 2). It shows the apex of the spine, the 

 hump (somewhat injured) and the region behind it. 



E 1909 (2) This spine lacks the apex, and the two faces are crushed 

 together in the hump region; but it shows the inferior 

 margin of the front half of the spine. Length, as far as 

 preserved, 78 mm. 



Formation and Locality. — Conodont bed (Genesee) ; Eighteen Mile 

 Creek, near North Evans, Erie County, N. Y. Collected by W. L. 

 Bryant. 



Spine about 9 cm. in length; depth at beginning of hump contained 

 about 3 times, and the part of spine behind hump about 3I times, in 

 the total length. Hump in profile view, gently convex above, and 

 descending to meet the post-hump portion of spine in a slight sigmoid 

 curve; hump, viewed from above, relatively broad (its posterior mar- 

 gin is not sufficiently preserved to show its entire outline) ; its height 

 less than the portion of the spine back of it. Upper margin of spine 

 gently concave, changing to gently convex toward the apex; "lower" 

 margin of apex almost straight. Sides of spine incised with short, 

 irregular lines and shallow grooves more or less parallel to the axis 

 of spine. 



Remark.— This species is known only by the two cotypes. These 

 are complete spines, but not well-preserved; between the two, how- 

 ever, the characters of the species may be fully made out. Plate 

 54, figure I, is a composite drawing based on the two specimens. 



The species is readily distinguished by the relatively straight apical 

 portion, which is not reflexed upward as in most species (for instance, 

 S. altonensis) ; and by the form of the hump, as well as its relative size 

 as compared with the post-hump portion of the spine. 



If we compare the present species with Stethacanthus spines from 

 later horizons, we are perhaps justified in regarding it as primitive or 

 generalized. This is shown by the fact that the apical portion of the 

 spine is straight, not recurved; in later forms this portion is gently 



