682 SCIENCE PROGRESS 



become longer and stouter, while in the sacral and anterior 

 caudal region the bases of the plates are approximated and 

 supported on the summits of the tall and expanded neural 

 spines. The terminal third of the tail seems, however, to have 

 formed a flexible aggressive weapon, in which the laterally 

 divergent spines were inserted in the muscles between the 

 neural spine and the centrum. Although the caudal spines 

 of the English Kimeridgian Omosaitrus are structurally identical 

 with those of one species of Stegosaurus, the author is indisposed 

 to admit the generic identity of the Old World and American 

 types, as vertical plates have not been discovered in the former. 

 In a note to Nature Dr. F. A. Lucas states that while Dr. Lull 

 believes the plates to have been arranged in pairs, his own 

 opinion is that although, reasoning by analogy, they should 

 have been thus arranged, the facts point to their having been 

 placed alternately on opposite sides of the median line. No 

 pair of plates has ever been found, and, making the greatest 

 allowance possible for individual variation, it seems incredible 

 that differences of several inches should exist between the 

 plates from the two sides of the body if they were arranged in 

 symmetrical pairs. 



Little work has been done among the more typical Crocodilia ; 

 but an unusually well-preserved crocodilian skull from the 

 Ceratops beds of Wyoming, in the United States National 

 Museum, has been referred by Mr. C. W. Gilmore, Proc. U.S. 

 Nat. Mus., vol. xxxviii. pp. 485-502, in spite of its later geological 

 horizon, to a second species of the genus Leidyosuchus, originally 

 described from the Judith River Beds of Alberta, Canada. The 

 new species is named L. sternbergii. A second skull, from 

 the Hell Creek beds of Montana, which came under the author's 

 notice after the original paper was written, is also described and 

 figured. 



Leidyosuchus is a short and broad skulled crocodile, with 

 the nasals apparently not reaching the nares, the posterior 

 nostrils enclosed by the pterygoids (instead of being behind 

 them, as in Crocodilus), the mandibular symphysis short and 

 formed in part by the splenial, the upper teeth more numerous 

 than the lower, the first lower tooth received into a pit, and 

 the third and fourth — which are about equal in size — into 

 notches in the skull. The centra of the vertebrae have the 

 cup in front ; and there was armour on the lower as well as on the 



