EASTMAN : CARBONIFEROUS FISHES FROM THB CENTRAL WKST. 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. trituigularis, and //. 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 obtiiiued 

 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 Physonemns, Erismacanthus (including Gam])sacan- 

 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- 

 (jerus 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'Cov. 



Very interesting stages of modification are displayed by the group of Pliy- 

 sonemus-like spines throughout tlieir existence iu 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 iu 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 ([uite rudimentary anterior 



1 Jaekel, 0., Ueber die Organisation dcr Petalodonten (Zeitsehr. deutsch, gcol. 

 Ges., Vol. LI., 1899, p. 285. 



