MORPHOLOGY OF THE COAL MEASURES AMPHIBIA. 27 



ture branchiate individual, some 47 mm. in length, of Diemyctylus torosus Esch., 

 from a fresh-water pond on Orcas Island in Puget Sound. The presence of this 

 species on the island is very suggestive. It is of extreme interest, too, that the con- 

 dition represented in the alimentary tract of the fossil branchiosaurs should resem- 

 ble so closely that of an immature rather than a mature form. 



(j) The vertebral column is clearly and readily separable into cervical, dorsal, 

 sacral, and caudal regions. The neck is always short, with from 5 to 10 vertebrae, 

 cervical ribs often present. The dorsal region is not long, but varies from 20 to 30 

 in the constituent vertebrae. There is a single sacral vertebra not always to be 

 readily distinguished from those of the dorsal and anterior caudal series. The tail 

 may be very short or extremely long, with neural and haemal spines elongate and 

 flattened into an oar-like appendage. The distal caudals are in some species car- 

 tilaginous, apparently always so in the Branchiosauria. 



(k) The atlas and axis are unknown among the American specimens, but we are 

 able to infer from the structure of the other vertebras what this must have been ; and 

 our inferences are partly confirmed by the conditions existing in the European forms 

 (187). The atlas, apparently, consisted of a pair of neurocentral plates which are 

 partly ossified, partly embedded in cartilage, judging from the edges of the plates 

 which have been preserved. The centrum seems not to have been present in 

 the atlas, or if present it was only very slightly developed and quite free from 

 the neural pieces and largely embedded in cartilage. A fairly accurate picture of 

 the condition of the atlas and axis may be seen on examining a cow, pig, or chick 

 embryo (378) in the early stages of vertebral development, which has been cleared 

 by the Schultze method (Amer. Journ. Anat., vil, No. 4, 1908). 



(7) The dorsal vertebra, as well as those of the other series, present a primitive 

 character (fig. 8) in the persistence of the notochord (540). Among the Branchio- 

 sauria the notochord was not at all or but slightly constricted intravertebrally, but 

 among the Microsauria it was constricted so far that the notochordal remnants in 

 each centrum resemble an hour-glass. 



The structure of the vertebrae among American forms agrees fully with that 

 outlined by Credner, Fritsch, and others for the European species. The details of 

 structure are so fully given by Zittel (642, pp. 34 6 ~353) and by Schwarz (540, 541) 

 that it will not be necessary to state more here as to their structure, since there is 

 nothing new to add concerning the American species. 



The temnospondylous vertebra of the same nature and type as exhibited by the 

 Permian forms has its representatives (94, 478) in the Coal Measures. Spondylcr- 

 pcton spinatum Moodie (478) (plate 4, figs, i, 2) and Eryops sp. (plate 18, fig. 2) 

 indicate the embolomerous and rachitomous types of vertebral structure. The 

 occurrence of these widely different types of vertebral structure indicates a long his- 

 tory for the group prior to the Coal Measures. This history is further indicated by 

 footprints in the Mississippian and Devonian of this continent. 



(m) The ribs (fig. 8) are very diverse in structure and in their mode of articula- 

 tion (541) with the vertebral column. The characters of the ribs and vertebne con- 

 stitute the best means of classification of these animals so far discovered. In the 



