THE TEMNOSPONDYLOUS AMPHIBIA. 



179 



the intercentrum and pleurocentrum, in the greater size, in the larger proportions 

 of the neurocentrum, and the greater proportionate size of the intercentra. 



Spondylerpeton spinatum Moodie. 



MOODIE, Kans. Univ. Sci. Bull., VI, No. 2, pp. 355-357, pi. 8, figs. I and 2; pi. 9, fig. i, 1912. 



Type: Specimen No. 793 (26) and obverse, Yale University Museum. 



Horizon and locality: Mazon Creek, near Morris, Illinois. 



The species is very imperfectly known. Sufficient is present, however, to show 

 its wide generic differences from other forms of the Cricotidae. These characters 

 are of a phylogenetic nature and indicate the more primitive nature of the present 

 form, as we would expect from its geological position. The sutures separating the 

 four vertebral elements are clearly ap- 

 parent. The pleurocentral-neurocentral 

 suture is apparent in 4 vertebrae. 



There is but a single pleurocentrum 

 preserved complete. This shows the 

 form of the attached neurocentrum and 

 chevron, which corresponds to the hypo- 

 centrum pleurale according to Fritsch. 

 The pleurocentrum is flattened laterally, 

 with a rather large canal for the noto- 

 chord. Its sides are marked with 4 

 longitudinal grooves. Surfaces for the 

 attachment of the ribs are not present, 

 and for this reason, as well as the pres- 

 ence of chevrons, the vertebrae are sup- 

 posed to be caudals. As such they rep- 

 resent an animal of some 3 or 4 feet in 

 length. It was the giant of the Mazon 

 Creek Amphibia. (Plate 4, figs. 1,2.) 



Attached to the upper side of 

 pleurocentrum by a sutural union occurs 

 the neurocentrum. The neural arch is quite large and is oval in outline, although 

 somewhat constricted at the tip. The spine of the neurocentrum is rather long and 

 broad at the base, measuring 12 mm. across the anterior zygapophysis. The neuro- 

 centrum is laterally flattened and ends in a rather acute and somewhat rugose 

 point. It was probably tipped with cartilage. The anterior zygapophysis occurs 

 well down on the neurocentrum, its lower edge being 5 mm. from the suture sepa- 

 rating the pleurocentrum and the neurocentrum. The posterior zygapophysis occurs 

 quite high up on the neurocentrum and lies at a distance of 15 mm. from the pleuro- 

 neurocentral suture, thus indicating an extreme posterior inclination of the neural 

 spine. The posterior zygapophysis of the best preserved vertebra is separated 

 from its mate, the anterior zygapophysis, in the next succeeding vertebra by a 

 space of 5 mm. 



FIG. 39. The vertebrae of Spondylerpeton spinatum 

 Moodie, the only known temnospondyle from the 

 the Mazon Creek shales. X I. hy, hypocentrum ; inc, 



intercentrum; pc, pleurocentrum; nc, neurocentrum. 



