EASTMAN: CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 211 



as Gainpsacautbus, Lecracanthus, ami Dipriacantlius appear to be of the same 

 general nature, and may be prov'isionally regarded as the dissociated anterior 

 branches belonging to Erismacanthus. The Kinderhook species of this genus 

 are small and exceedingly primitive as compared with the highly ornamented 

 spines occurring in the St. Louis limestone, some of which attain the astonish- 

 ing length of over 20 cm., and are provided with very large-sized denticles 

 along the anterior arm. The forms included under this genus are referable to 

 the head region with even greater certainty than those of Physonemus, and 

 evidently occurred in pairs, whereas the latter would seem to have occupied a 

 median position. 



Erismacanthus barbatus, sp. hot. 



(Plate 5, Fig. 47-) 



Type. — Isolated and fragmentary spine; Museum of Comparative Zoology. 



Spines small, very much laterally compressed, smooth or with faint longi- 

 tudinal striae, and without denticles or tuberculations of any kind. Principal 

 portion of spine gently arched, gradually tapering, and giving off two spiniform 

 branches of unequal size from the convex margin. 



This peculiar and in many respects primitive form of Erismacanthus is 

 known by the solitary example shown of the natural size in the accompanying 

 figure. It is excessively flattened, and consists of a gently arched portion 

 corresponding to the denticulated posterior branch of other species, and of two 

 rudimentary anterior branches, each with a thickened border and elevated 

 ridge. A slight diff'erentiation in the superficial ornament, which in later 

 species becomes very pronounced, is already indicated in this early form, in 

 that the main or posterior branch is feebly striated and the two anterior pro- 

 jections quite smooth. 



Formation and Locality. — Kinderhook limestone ; Burlington, Iowa. 



Erismacanthus maccoyanus St. John and Worthen. 



1875. Erismacdtitkits macroyanus St. John and Wortlien, Pal. Illinois, Vol. VI., 

 p. 461, PI. XXII., Figs. 1, 2, 4 {mn Fig. 3). 



This species has been known hitherto by only a few very diminutive spines 

 from the St. Louis limestone, none of the specimens in the hands of Messrs. St. 

 John and Worthen exceeding one inch in length. Whether all of the examples 

 figured by these authors pertained to a single species was indeed questioned by 

 them, on account of differences in the form and arrangement of the posterior 

 denticles. Their views concerning the imperfect spine shown in Plate XXII., 

 Fig. 3, of the seventh volume of the Illinois Palaeontology are thus expressed : 

 " Whether the approximate arrangement of the denticles observed in the above 

 specimen is imlicative of s])ecific distinctness from its associates we have not 

 the means for determining; it is, however, probable that these closely arranged 



