THE PERMIAN FISHES OF NORTH AMERICA 167 



Cope's description of Gnathorhiza was given in a single paragraph, which 

 was unaccompanied by figures, and otherwise left doubts open concerning 

 the diagnostic characters of this form; for one reason, because of his com- 

 parison of these dental elements with sharks' teeth. It would have been diffi- 

 cult to recognize his genus again merely by his description had it not been 

 for the preservation of his type specimen in the American Museum of 

 Natural History. Before any figures of it were published, however. Dr. 

 Eastman described two similar dental elements under the name Sagenodus 

 pertenuis (SO b). He recognized the anomalous character of this dipnoan, and 

 gave an accurate description of its dental elements accompanied by excellent 

 figures. His view of the peculiarities of this type of dipnoan dentition is 

 given in these words : 



[This fish] "occupies a unique position amongst fossil dipnoans in having 

 a dentition adapted for cutting instead of crushing, thus paralleling the con- 

 ditions found in certain Palaeozoic sharks and in recent Gymnodonts. This 

 divergence is the more striking in view of the singularly uniform type of dental 

 system pervading lung-fishes throughout their entire geological history." 



In 1908 the writer figured the type specimen of Gnathorhiza for the 

 first time and called attention to its identity with the form described as 

 Sagenodus pertenuis by Eastman (55 a) . 



Of the dental elements referable to Gnathorhiza, three distinct species 

 have been made: 



1. Ctenodus pusillus Cope, 1877, based on a very small dental plate 



from Illinois. 



2. Gnathorhiza serrata Cope, 1883, based on a small dental plate 



from Texas. 



3. Sagenodus pertenuis Eastman, 1903, based on two small dental 



plates from Illinois (J). 



A study of the types of these species, however, shows that they are all 

 of the same genus {Gnathorhiza), and probably of one species. For this 

 species the name pusilla should be retained because of priority. A differ- 

 ence is observable between the pusilla and the serrata forms — the former 

 having two and the latter but one transverse coronal ridges. This, however, 

 is not sufficient reason for separating them specifically, since variations 

 in the number of ridges in dipnoan dental elements is quite common. 

 Furthermore, as remarked by Dr. Eastman, it is probable that the superior 

 dental plate of this form had one ridge more than the lower. 



The generic characters of Gnathorhiza are comprised in the description 

 of G. pusilla, the only known species, below: 



Gnathorhiza pusilla (Cope). (Plate 27, figs 9-10.) 



1877. Cunodus pusillus Cope, Proc. Amer. Philos. Soc, xvii, p. 191. 

 1883. Gnathorhiza serrata Cope, Proc. Amer. Philos. Soc, xx, p. 629. 

 1888. Gnathorhiza serrata Cope, Trans. Amer. Philos. Soc, xvi, p. 286. 

 1891. Sagenodus pusillus (Cope), Woodward, Cat. Fos. Fishes, Brit. Mus., 11, p. 261. 

 1899. Sagenodus pusillus (Cope), Williston, Kans. Univer. Quart., Ser. A, viii, p. 176. 

 19CX3. Sagenodus pusillus (Cope), Case, Journ. Geol., viii, p. 705, pi. i, figs. 9a, 9*. 

 1903. Sagenodus pertenuis Eastman, Amer. Nat., xxxvn, p. 493, figs. 1-2. 

 1908. Gnathorhiza serrata Cope, Hussakof, Bull. Amer. Mus. Nat. Hist., xxv, p. 53, 

 fig. 25. 

 Type: A small right palatal plate. No. 6508 University of Chicago 

 Gurley Collection. Vermilion County, Illinois. 



