Geology and Mineralogy. 85 



relationship, these forms are not far from the Proterosauria and 

 Proganosauria, but differ from the former in the higher degree 

 of ossification, especially of the pelvic and pectoral girdles, and 

 from the latter in the lack of adaptation to a water life. The 

 most striking feature of the group is the enormous development 

 of neural spines to which it is impossible to assign any utilitarian 

 value. The animals were fiercely carnivorous, with enormous 

 teeth. The spines may be mere exuberance of growth from 

 a possible utilitarian beginning ; they may be an illustration of 

 Beecher's law that the development of spines and excrescences 

 accompanies the approaching extinction of a group. 



Geographically, the Pelycosauria are distributed in north cen- 

 tral Texas and some of the adjacent states and in Illinois ; also in 

 Prince Edward's Island. Abroad they occur in Bohemia and, 

 less certainly, in centi*al Germany and in France. The remains 

 always occur mingled with an abundant fauna of fishes, amphib- 

 ians, and other reptiles. 



Geologically, the suborder is confined in North America en- 

 tirely to the Permian, though in Europe Gtenosaurus, an ally of 

 JSfaosanrus and Dimetrodon, is found in the Muschelkalk. An 

 ample bibliography of 141 titles closes the work. r. s. l. 



9. The Skull of J3rachauchenius, with observations on the 

 relationships of the Plesiosaurs • by Samuel W. Williston, 

 Proc. IT. S. National Museum, vol. xxxii, pp. 477-489, with plates 

 xxxiv-xxxvii. — The type specimen of the genus and species 

 under consideration comes from the Benton Cretaceous of West- 

 ern Kansas and is distinguished from other plesiosaurs by several 

 remarkable characters, in particular the union of the palatine 

 bones in the middle line, and the very short neck. 



In discussing the relationship of the Plesiosaurs, Professor 

 Williston refers to certain marked resemblances in form and 

 mode of progression between the oar-propelling plesiosaurs and 

 turtles, as conti'asted with the tail-propelling type represented by 

 the ichthyosaurs, mosasaurs and thalattosuchians which Fraas 

 uses as a support for the diphyletic grouping of the Reptilia by 

 Osborn. These resemblances Williston thinks no more imply 

 a common phyletic origin than do the much more marked resem- 

 blances of the ichthyosaurs and dolphins. He further states that 

 there is only a remote relationship between the two orders (turtles 

 and plesiosaurs) in osteological structure, and is still strongly of 

 the opinion that the Sauropterygia were derived from a primitive 

 therocephalian ancestry ; the turtles having had a quite inde- 

 pendent origin from some primitive cotylosaurian, like the Chely- 

 dosauria. The turtles occupy a phylum distinctly their own, no 

 more intimately related to the plesiosaurs than they are to the 

 ichthyosaurs or rhynchocephalians, and the ichthyosaurs, too, 

 enjoy a geological line from the most primitive type of reptiles, 

 and should no more be grouped with the dinosaurs and croco- 

 diles than with the plesiosaurs and theriodonts. r. s. l. 



