THE PERMIAN FISHES OF NORTH AMERICA l6l 



This species is not well diflFerentiatcd from the preceding, owing to the 

 paucity of material. No sufficient reason for separating it can be found in 

 the peculiarities said by Cope to be present in the teeth — as has already been 

 pointed out by Broili (7). The material available indicates a form of larger 

 size than Diacranodus texensis. Its distinctive characters as given by Cope 

 are the following: 



Original description: "The lower jaw is distinguished from that of the 

 D. compressus by its small transverse as compared with its other diameters. 

 The ramus is quite compressed, and is not thicker at the inferior edge than 

 the superior, and is slightly concave on the inner side. Its external face 

 is nearly vertical. The angle is rounded forwards, and there is no angle 

 behind the cotylus, which is raised above the superior line of the ramus. 

 The cotylus is rather large, and has a shallow anterior superior, and a pos- 

 terior subposterior facet. There is no indication of a coronoid process. The 

 inferior edge of the ramus is swollen on the outer side, below the anterior 

 border of the condyle, so as to mark with the thickened posterior edge of 

 the ramus a fossa in the position of the masseteric." 



ICHTHYODORULITES. 



Genus CTENACANTHUS Agassiz. 



Poiss. Fos., Ill, 1837, p. 10. 



A provisional genus of sharks, to which are referred numerous paleo- 

 zoic dorsal fin-spines, known to have had (at least in certain species referred 

 to the genus) cladodont dentition and primitive fin-fold paired fins. 



Revised description of genus: 



1. Dorsal spines straight or gently arcuate, and more or less later- 



ally compressed. 



2. Lateral faces longitudinally ridged, the ridges smooth or orna- 



mented with various types of denticulations or beading. 



3. Posterior face flat or concave, usually with a series of small 



denticles along each margin. 



Ctenacanthus amblyxiphias Cope. (Plate 30, figs. 6-6a.) 



1891. Ctenacanthus amblyxiphias Cope, Proc. U. S. Nat. Mus., xiv, p. 449, pi. 



xxviii, fig. 3. 

 1902. Ctenacanthus amblyxiphias Cope, Hay, Bull. U. S. Geol. Surv.,No. 179, p. 327. 



Type: An imperfect spine. When complete about 25 or 30 cm. No. 

 7283 Am. Mus. Texas. Referred specimen: No. 7282 (plate 30, fig. 6). 



Original description: "Spine elongate, but little curved, moderately 

 compressed; the posterior face with a flat median plane bounded by a shallow 

 groove on each side. The ridges are wider than their interspaces, and they 

 gradually become smaller posteriorly, so as to be half the diameter of the 

 anterior ribs. The anterior border consists of a single rib of twice the diam- 

 eter of the largest lateral ribs. Its front surface is smooth; the sides are 

 marked with shallow grooves directed downward, and the border is serrate 

 with subacute tubercles, which point backward. The tubercles of the ribs 

 are closely placed and vary from round to transverse in shape, and have 

 a finely grooved surface. The line of the posterior hooks is flush with the 

 sides of the spine. They are small, decurved, and subacute. ' ' 



