GEOLOGICAL SURVEY OF THE TERRITORIES. 423 



sists, I believe, of the adjacent rays or compound ray forming the mar- 

 gin of the caudal fin. This finds support in the analogous structures 

 already mentioned as occurring in Ulops, and the extinct genus Prym- 

 netes* Siluroids, &c, and the resemblance of the pectoral spine to the 

 same weapon of the latter group adds to the probability of the correct- 

 ness of this conclusion. 



These remarks are made because Professor Agassiz, in the Poissons 

 Fossiles, has referred several spines to the Gestraciont genus Ptychodus, 

 which are very similar in character to that described above as the anal 

 or caudal support of iSaurocephalus thaumas. These were derived from 

 the upper cretaceous chalk of Kent, England, where Ptychodus teeth 

 also occur. The Saurocephalus teeth, described by Professor Agassiz 

 in the same work, were, however, derived from the same chalk and the 

 same locality, and, from what has preceded, I believe the segmented 

 spines should be referred to the latter genus rather than to Ptychodus. 

 This is the more probable, in view of the fact that Professor Mudge did 

 not procure a single Ptychodus tooth during his exploration. 



APSOPELIX, (Cope.) 



Established on the remains of a fish preserved on a block of clay. It 

 presents its ventral aspect, and displays pectoral, ventral and anal fins, 

 with the series of interneural spines to which the dorsal radii were ar- 

 ticulated. 



The scales are large and cycloid. They do not present a trace of ra- 

 dii, but are marked with fine and close concentric grooves. These as- 

 sume a vertical direction on the exposed surface, and are there more 

 irregular 5 the more marginal ones terminating above and below. Bat 

 few and central grooves are truly circular. No abdominal carina. 



The two pelvic bones are together truncate heart-shaped, the acumi- 

 nate apex presented forward. Their posterior portion is a strong trans- 

 verse rib; anteriorly each is a thin plate, with thickened outer edge, 

 uniting with its fellow on the median line. The median portion is so 

 thin as to be readily broken away. The ventral fins are short and 

 wide, with numerous rays. The coracoid bone is a broad lamina, and 

 the pectoral fin evidently bad the support of rod-like humeral bones of 

 no great length, after the type of most Physostomous fishes, but their 

 form cannot be made out. Pectorals not elongate. The anal fin origi- 

 nates but a short distance behind the ventrals, and was not armed 

 with an anterior spine ; its length cannot be made out. Immediately 

 above it a dorsal fin, with slender rays, is represented by the bases of 

 these rays. From above the ventrals to above the distal portion of the 

 pectorals a line of projecting points appears in tho, specimen, which I 

 am disposed to ascribe to the articular portions of the interneural spines 

 and attached fin rays of a first dorsal, but of this I cannot be entirely sure. 



The vertebrae are longer than deep, and present the two deep lateral 

 grooves frequently seen. The number in the cervico-abdominal series 

 is twenty-six. The ribs are delicate, and supernumerary ribs are present. 



In comparing this genus with forms already known, points of distinc- 

 tion from all of them may be detected. Thus, the lack of pectoral spine 

 will distinguish it from the known genera of Saurodontidm at least. The 

 character of the dorsal fin distinguishes it from Characinidcc, Salmonidce, 

 &c, which, with the scales, point toward Clupeidce and Elopidcv. Prom 

 these the form of the pelvic bones distinguishes it. 



The ends of both muzzle and caudal region are destroyed. The latter 



* Cop<5 Proc. Am. Phil. Soc, March, 1871. 



