xo. 2177. FOSSTL FISHES TN XATIONAL MUSEUM— EASTMAN. 245 



HETERACANTHUS UDDENI Lindahl. 



Plate 1. 



Heteracanthus uddeni Lindahl, Jouni. Cincinnati Soc. Nat. Hist., vol. 19, 1895 

 p. 95, pi. 6. 



The spines of this species are less abundant than those of the coeval 

 H. 'politus, which have a different general outlme and a relatively 

 coarse ornamentation. The type-specimen serving for the establish- 

 ment of this species, now preserved in the Museum of the Cincinnati 

 Society of Natural History, has the external surface partly denuded 

 and is defective in preservation as regards the basal portion and an- 

 terior margin. Up to the present time, however, it has remained 

 the most complete fin-spine of the species and genus thus far brought 

 to light. During the past year a larger and still more perfect speci- 

 men has been found in the Cedar Valley limestone near Iowa City, 

 Iowa, by Prof. Abram O. Thomas, of the State University, and placed 

 in the writer's hands for stud3^ It is shown of the natural size in 

 plate 1. 



The posterior or convex margin of the newly discovered spine is 

 more strongly arched than in the type-specimen, and the distal por- 

 tion is forwardly curved to a slight degree. On the other hand the 

 anterior margin is not developed so strongly as to form a projecting 

 shoulder toward the base, which is the case to a certam extent in the 

 type-specimen, and in which respect an approach is mdicated to the 

 conditions observed in Stethacanthnis and Lower Carboniferous spe- 

 cies of Oracanthus. Nevertheless, the character of the ornamentation 

 is practically identical with that of the original upon which the spe- 

 cies is founded, and for that reason we are disinclmed to regard the 

 two spines as specifically distinct. In the specimen here figured, the 

 entire outline of the inserted portion of the base is distinctly shown, 

 and the resemblance of the inserted part to the base of Chimaeroid 

 head-spines, and also those of Carboniferous forms like Physonemus, 

 etc., is obvious. It is probable that the dermal defenses of this 

 nature occupied a position immediately behind the head. 



Formation and locality. — Cedar Valley limestone (Middle Devo- 

 nian) ; Johnson county, Iowa. 



DIPNOI. 



Family CTENODONTIDAE Traquair. 



Genus DIPTERUS Sedgwick and Murchison. 



The earliest known occurrence of Dipterine remains in this country 

 is that of a dental plate of Dipterus itself wliich has been described 

 within the last few years from the Columbus limestone (Middle 



