EASTMAN :- CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 205 
tically from the angle where they meet to the coronal apex. Lateral expan- 
sions of crown short, slightly tumid at their extremities. 
The tooth represented in the accompanying figures, which corresponds to 
the above description, is of the same general form as those known under the 
names of Helodus coxanus Newb., H. triangularis, and H. acutus Davis, all of 
which may be referred with little hesitation to the symphysial series of Coch- 
liodont sharks. The slightly recurved apex in the species under discussion 
indicates that the series was feebly prehensile, and the triangular excavation 
to which the trivial title has reference, together with markings on the anterior 
face, show that the individual teeth of the series were very closely applied and 
slightly overrode one another. One other specimen, besides that shown in the 
figures, is preserved in the Cambridge collections, both having been obtained 
from the Subcarboniferous limestone of Salem, Indiana. 
Formation and Locality. — Subcarboniferous ; Salem, Indiana. 
ICHTHYODORULITES PRESUMABLY REFERABLE TO 
COCHLIODONTIDAE. 
The most plausible interpretation which has been given of the peculiar Ich- 
thyodorulites known as Physonemus, Erismacanthus (including Gampsacan- 
thus and Lecracanthus), Dipriacanthus, and certain forms of Oracanthus, is that 
they are head-spines corresponding to those already observed on either side of 
the head in the Permian Menaspis, and in one example of Oracanthus armi- 
gerus Traquair from the Calciferous sandstone of Eskdale, Dumfries. In our 
opinion the genus Stethacanthus should be placed in the same category with 
the above, and all these forms may be provisionally grouped with the Coch- 
liodontidae. Various forms of Physonemus spines are arbitrarily distributed 
between Petalodus and Polyrhizodus by Jaekel,! but the evidence of actual 
association of parts, which is necessary for the confirmation of this conjecture, 
has not yet been forthcoming. 
PHYSONEMUS M’Coy. 
Very interesting stages of modification are displayed by the group of Phy- 
sonemus-like spines throughout their existence in the Lower Carboniferous. 
The earliest and most primitive forms of Physonemus itself are found in the 
Kinderhook accompanied by small forms of Stethacanthus. The only known 
species, those described in the following pages, are of diminutive size, hook- » 
shaped, and nearly destitute of surface ornamentation. Erismacanthus is also 
represented in the Kinderhook by two small comparatively unornamented 
species, and it is noteworthy that these have quite rudimentary anterior 
1 Jaekel, O., Ueber die Organisation der Petalodonten (Zeitschr. deutsch, geol. 
Ges., Vol. LI., 1899, p. 285. 
