The genus is based on a specimen consisting of 9 imperfect vertebræ, from the caudal region of a relatively large amphibian. The present genus exceeds _Diplospondylus_ from the Gaskohle of Bohemia (251) by twice its size and is about two-thirds the size of _Cricotus heteroclitus_ Cope (98) from the Permian of Kansas. The vertebræ are twice as high as wide, differing thus from _Cricotus_, in which the vertebræ are nearly circular. A character which is of great importance is the large size of the intercentrum, which almost equals the pleurocentrum in size. It is similar to the pleurocentrum in shape, except for the attached neurocentrum and chevron on the latter. The present genus differs from _Diplospondylus_ in the greater length of 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, pl. 8, figs. 1 and 2; pl. 9, fig. 1, 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 Cricotidæ. 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 apparent. The pleurocentral-neurocentral suture is apparent in 4 vertebræ. [Illustration: Fig. 39. The vertebræ of _Spondylerpeton spinatum_ Moodie, the only known temnospondyle from the the Mazon Creek shales. × 1. _hy_, hypocentrum; _inc_, intercentrum; _pc_, pleurocentrum; _nc_, neurocentrum.] There is but a single pleurocentrum preserved complete. This shows the form of the attached neurocentrum and chevron, which corresponds to the hypocentrum pleurale according to Fritsch. The pleurocentrum is flattened laterally, with a rather large canal for the notochord. 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 presence of chevrons, the vertebræ are supposed to be caudals. As such they represent an animal of some 3 or 4 feet in length. It was the giant of the Mazon Creek Amphibia. (Plate 4, figs. 1, 2.)