358 PALEONTOLOGY OF OHIO. 



able in many portions of the skeleton. Most of the order exhibit three 

 thoracic shields, but some species seem not to possess them, e. g., those of 

 the genus Oestocephalus. The same may be said of the osseous rods or 

 scuta of the belly, which I can not find in the snake-like forms, and in 

 a few others. The spines of the vertebrae may be enlarged and orna- 

 mented with sculpture, as in Thyrsidium, Ptyonius, and others. The 

 genera in which no osseous vertebrae have yet been discovered are Colos- 

 teus and Amphihamus. 



III. DISTRIBUTION OF THE STEGOCEPHALI IN TIME AND SPACE. 



Species of this order have been discovered in all of the primary faunal 

 regions of the earth excepting South America. In time they first ap- 

 pear in the Coal Measures, and continue through the Permian, the 

 RhsBtic, and the Trias. The first formation has yielded the greatest 

 number of species, and the Trias is the next most productive of them. 

 The following table is copied from the report of a committee of the Brit- 

 ish Association for the Advancement of Science, of which L. C. Miall is 

 chairman, as expressing in a succinct manner the distribution of these 

 animals in time and space. Additions and a slight correction appear in 

 the North American department. The genus Salamandrella, Gaudry, is 

 omitted, since its describer thinks that it belongs to the Urodela; for a 

 similar reason the genus Cocytinus is omitted. 



