l6o THE PERMO-CARBONIFEROUS RED BEDS OF 



dental groove, possibly on the anterior end of the coronoid, but the outline 

 of this bone can not be made out. The outer surface of the jaw is sharply 

 reticulate. The sutures of the posterior end of the jaw can not be made out, 

 but the general form is shown in figure 33. The most surprising thing about 

 the jaw of Cricotus is the small size of the teeth and their peculiar form; 40 

 teeth of small size can be counted in the large jaw and there is no indication 

 in this jaw, nor in any of the fragmentary ones recovered, of larger teeth at 

 the anterior end. The teeth are long and slender, with broad bases fused to 

 the edge of the dentary, but rapidly contracting to a cylindrical form. The 

 apex is chisel-shaped, with the cutting-edge running fore and aft and the 

 whole edge slightly moved. to the rear, so that the posterior edge overhangs 

 the posterior edge of the body of the tooth (fig. 34). The dental series occu- 

 pies a deep groove formed by the dentary and the splenial and coronoid (?). 



Vertebrae. — Of the numerous vertebra fotmd only two, intercentra and 

 centra, were fomid in position; these are from the caudal series. The inter- 

 centra are fully as thick as the centra and very similar to them in appearance. 

 The neural arches are anchylosed to the intercentra, at least to the elements 

 which bear the chevron bones. In the figures published previously by Cope 

 and Case the netiral arch is shown directly above the chevron-bearing ele- 

 ment and apparently supported by it; this is as the vertebra; appear in the 

 specimens in the American Museum in New York; in the vertebrae in this 

 collection the neural arches are in sutural connection with the elements bear- 

 ing the chevrons and there can no longer remain any doubt of their position. 

 The same condition is found in other stegocephalians. 



It has been generally thought that the intercentra of the dorsal region 

 were much thinner than the centra; thin disks regarded as intercentra are 

 not uncommon in most collections from Texas, but few have been found in 

 position. In the American Museum collection there is a sacral series with 

 a thin disk directly posterior to the last sacral centrum (fig. 51 e, Publication 

 No. 146, Carnegie Institution of Washington), but without chevron or neural 

 arch. Abundant thin disks with and without chevrons occur in all collections 

 from Texas. The author is of the opinion that the thin disks without processes 

 are pygal intercentra and that immediately following them in the anterior 

 caudal region there are thin intercentra which bear chevrons. The tail was 

 proportionately very long and strong and both the intercentra and the centra 

 became elongated in the middle of the series, something after the manner 

 of the mid-caudal vertebras of the Eocene cetacean Basilosaurns. In this 

 mid-caudal region the intercentra became as long as the centra and came to 

 bear the neural arches as well as the chevrons. 



Other thin disks with short diapophyses are believed to belong in the 

 cervical series. 



From the fact that the thin disks can be located with considerable cer- 

 tainty in the cervical and caudal series, and that they are in the minority in 

 all collections, the author is inclined to the belief that the dorsal intercentra 



