198 LEA'S DESCRIPTION OF A FOSSIL SAURIAN 



Sandstone of Shropshire."* This description would almost answer for the vertebras 

 of our Clepsysaurus, and it would seem that this was the prevailing structure of this 

 important portion of the frame of the reptiles of that period. 



Having given the facts connected with the condition of the " New Red Sandstone" 

 of this country, so far as ascertained, and stated the views of various geologists on the 

 subject, I shall proceed 1o the consideration and description of the saurian bones 

 found by Dr. Shelley in Lehigh county, now in the cabinet of the Academy, and I 

 acknowledge with thanks the kind assistance of my friend Dr. Leidy. 



In the examination of these interesting remains, we are naturally led first to 

 consider their analogies. The epoch in which they were animated, and moved on 

 oozy shores, has been remarked for the small amount of animal life which must have 

 then prevailed within the area of the sedimentary matter forming this deposit. 

 Organic forms of Palseozoic life had changed, in a measure, — a new phase was 

 making its appearance ; in fact, a new order of things was in preparation. In the 

 carboniferous period the immense growth of vegetable matter which must have 

 covered the areas now forming our coal fields, ceased longer to produce these vast 

 store houses of carbon. They were finished. The animal life that peopled the 

 waters, and the fauna which lived on the soil at that time, no longer existed — all was 

 becoming changed. An advance in organization was to be made — mesozoic, or 

 secondary life was to assume its sway. We, therefore, naturally find very little in 

 previous organisms to establish homologies. In plants the forms had changed ; in the 

 fishes the heterocercal tail was becoming less oblique ; in the reptilia we have only 

 the foot-marks, and a few imperfect bones of saurians, to compare with. For 

 analogies, therefore, we must rather look to the superior deposits, where reptilian life 

 became so prevalent, viz: the Lias, Oolite, etc., there the Teleosaurus, JElodon, etc., 

 among the Crocodilidce, and various genera of the Megalosaurinida, presented species 

 of great size and extraordinary abundance, becoming the monarchs of these periods. 

 All these present an advance in their organic structure, passing from the bi-concave 

 system of the vertebrae to the more perfect concavo-convex system. f 



GENUS CLEPSYSAURUS, Lea. 



The characters of this genus are derived from the form of the vertebrae and the 

 teeth. The name is given from the remarkable form of the centrum of the vertebrae, 

 which are very much compressed laterally towards the centre. The teeth are 

 minutely serrated on the posterior edge, but the serratures are not continued to the 

 apex, the superior portion becoming cylindrical. The anterior portion towards the 

 base is flattened, presenting at this part a gibbous form. 



• Mono. Permian Fossils, p. 237. f Since the above was in type, I have received from Mr. W. Struthers a 



large block of this Limestone conglomerate, from Plymouth, 13 miles N. AVest of Philadelphia. I believe it has 

 not been before observed on the south side of the New Red Sandstone, 



