418 GEOLOGICAL SURVEY OF THE TERRITORIES. 



posterior truncate. The section is lenticular, with a deep rabbet on one 

 side of the posterior edge ; section at the base circular, apex lost. The 

 sculpture consists of fine longitudinal raised striae, which bifurcate and 

 send numerous similar ridges to the teeth of the anterior margin. It is 

 probably a spine of a pectoral fin. It is identical in form and sculpture 

 with that described by Leidy as Xiphactinus audax, but differs in spe- 

 cific details. 



M. 



Long diameter of spine 0.0245 



Basal diameter of spine 019 



Length, to cervicals, (not distorted) 033 



Diameter of the anterior 021 



Length of a dorsal 016 



Length of a caudal 014 



Width of neural spine of caudal, at base -012 



Length of alveolar margin premaxillary 022 



Length of anterior margin premaxillary 02 



Depth from condyle of maxillary 026 



Length of crown premaxillary tooth 0042 



Diameter of crown premaxillary tooth 002 



A fragment of a large flat bone exhibits very delicate radiating 

 grooves, which are marked by spaced impressed dots. 



From the upper cretaceous of Kansas, six miles south of the town of 

 Sheridan. Professor B. F. Mudge. This species was about two-thirds 

 the size of the species last described. 



SAUEOCEPHALXJS ATJDAX, (LEIDY,) Sp. 



(Xiphactinus audax, Leidy. Proc. A. N. Sci., Phil., 1870, 12.) 



Established on a pectoral spine, supposed by Leidy to be that of a 

 siluroid. According to the description, it does not differ from that of 

 S. prognathus in more than specific characters. Thus the anterior mar- 

 gin is weakly serrate in the latter, a feature not described by Leidy in 

 the former. In S. audax the posterior portions of both sides are said to 

 be grooved ; in that part of the spine of 8. prognathus preserved, one 

 surface only exhibits the groove in question, one of whose edges is ob- 

 liquely ridged, as in S. audax. From Kansas 5 museum Smithsonian. 



SATJROCEPHALTJS THAUMAS, (COPE*) 

 (Proc. Amer. Philos. Soc, Nov., 1870.) 



This is larger than any of the species here described. It is represented 

 by wholes or j)arts of from seventy to eighty vertebrae, with numerous 

 neural and haemal spines and fin radii, and perhaps some ribs. There are 

 no teeth nor cranial fragments. The bulk of the vertebra? is double that 

 of those of S. phlebotomus, and appropriate to an animal of the size of the 

 S. lanciformis. It may be ultimately found to be identical with that 

 species ; but there is no evidence conclusive of such a view at present 

 in my possession. 



The vertebras present the usual two inferior, two lateral, and two 

 superior grooves — the last for the neural arch. There are no cervical 

 vertebrae, for these characters show them all to be dorsals and caudals. 

 The suture for the neurapophyses forms a regular angulate convexity 

 projecting downward. The arch is not closed above anteriorly, and is 

 expanded laterally, while the spine is directed very obliquely backward. 

 The concavities of the articular extremities are equal in the dorsals; but 



