EASTMAN: CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 211 
as Gampsacanthus, Lecracanthus, and Dipriacanthus appear to be of the same 
general nature, and may be provisionally 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. 
Hrismacanthus barbatus, sp. nov. 
(Plate 5, Fig. 47.) 
Type. — Isolated and fragmentary spine; Museum of Comparative Zodlogy. 
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 differentiation 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. 
Hrismacanthus maccoyanus St. Joun and Worrtuen. 
1875. Erismacanthus maccoyanus St. John and Worthen, Pal. Illinois, Vol. VI., 
p. 461, Pl. XXII, Figs. 1, 2, 4 (non 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 indicative of specific distinctness from its associates we have not 
the means for determining; it is, however, probable that these closely arranged 
