SS eee 
EASTMAN: CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 217 
been considerably removed by chemical decomposition, yet where the surface 
is preserved it is seen to be covered with vascular impressions extending well 
up toward the superior margin, thus indicating that the spine was deeply 
implanted. 
Formation and Locality. — Kinderhook; Iowa. Waverly sandstone ; 
Michigan. 
Stethacanthus erectus, sp. nov. 
(Plate 3, Fig. 29.) 
Type. — Imperfect spine ; United States National Museum. 
A species of about the same size as S. depressus, and differing from it in hav- 
ing the concave margin more abruptly curved, the exserted portion rising into 
a narrow and acuminate apex. 
It is unfortunate that the specimen selected as the type of this species is not 
more pertectly preserved, as it seems to represent an intermediate stage in the 
modifications affecting the exserted portion of these peculiar spines, being in 
fact transitional between low forms like S. compressus, S. carinatus, S. depressus, 
etc., and those in which the apex is recurved, like S. proclivus and S. altonensis. 
The anterior shoulder and greater part of the basal portion of this unique 
specimen have been broken away, but it is probable that the complete outline 
would show that the base was produced for some distance posteriorly beyond 
the hinder wall of the summital portion, as in S. altonensis and some other 
species. The total height of the part preserved is 3 cm., thus indicating a 
species of about the same size as the preceding. 
Formation and Locality. — Kinderhook limestone ; Lowa. 
CESTRACIONTIDAE. 
HOMACANTHUS Aeassiz. 
This genus, which is evidently closely akin to Ctenacanthus, is thus defined 
by A. S. Woodward: “Dorsal fin-spines of small size, slender, more or less 
arched, laterally compressed, and gradually tapering distally; sides of exserted 
portion ornamented with few, large, smooth, widely spaced longitudinal ridges ; 
a similar ridge also forming a large anterior keel ; posterior face with a double 
series of large, downwardly curved denticles.” The only American species 
that have been referred to Homacanthus have since been removed to other 
genera, but true representatives of this genus are apparently indicated by the 
spines described in the following paragraphs. 
