1862.] MARSH EOSATJRTJS ACADIANT7S. 55 



differences are seen in the absence of costal articular surfaces from 

 the sides of the centrum, in the deeper concavities at the vertebral 

 extremities, and in the form and dimensions of the superior arch 

 in this fossil. It was therefore concluded that the points of simi- 

 larity between it and the Ichthyosauri, which it most resembles, 

 clearly indicate that they belong to the same natural group of 

 marine reptiles, and to the same order; while the differences 

 which exist between them seem to be sufficiently numerous and 

 important to authorize the conclusion that they are generically 

 distinct, as might naturally be expected from the vast periods of 

 time that separated their existence. 



Habits of the Eosaurus. — These vertebras of the Eosaurus, although 

 the only remains of the genus at present known, are so characteristic 

 and well preserved that Mr. Marsh considers them sufficient to indi- 

 cate that the animal, like the later Enaliosaurians, was of great size, 

 air-breathing, cold-blooded, and carnivorous; that it was aquatic, 

 and probably marine, inhabiting the sea or estuaries, or, possibly, as 

 might be inferred from the place of its entombment, the mouths of 

 rivers flowing into the sea. The flattened form of the vertebras, the 

 great depth of their terminal concavities, the separate condition of 

 the neural arch, and its short longitudinal extent at the base, were 

 stated to be all consistent with the conclusion that the Eosaurus was 

 capable of rapid progress through the water in pursuit of its prey, 

 which was probably fishes ; and since it had then, according to our 

 present knowledge, no superior in point of size, it probably reigned 

 supreme in the waters of the Carboniferous era. 



Chemical examination. — Mr. Marsh observed that a comparison 

 of the composition of recent and fossil bone is interesting, both in a 

 chemical and a physiological point of view, and has already attracted 

 some attention. As he considered it desirable to add to the limited 

 data on this subject hitherto collected, he analysed a portion of a 

 vertebra of the Eosaurus, and the results were given in full. 



A preliminary qualitative examination showed the presence of 

 iron, manganese, copper, alumina, lime, magnesia, potash, soda, 

 organic matter, and water, as well as fluorine, chlorine, and sulphur, 

 with silicic, carbonic, phosphoric, and sulphuric acids. The com- 

 plete separation of these various constituents was necessarily attended 

 with some difficulty, and the methods resorted to were therefore 

 fully described, and a table showing the percentage of each consti- 

 tuent substance was given. 



A nitrogen- determination was made with a portion of the fossil of a 

 rather different character, which gave -776 per cent, for the amount of 

 that substance in it. This corresponds essentially with the results 

 obtained by M. Delesse, who has made some extensive researches 

 on this point, and who considers that the quantity of nitrogen 

 in fossil bones is, within certain limits, a reliable indication of their 

 age. The above-mentioned percentage of nitrogen is much greater 

 than that indicated by the analysis, and was probably due in part 

 to the substance used in the two cases being somewhat different ; 

 but part of the nitrogen in the determination may have been derived 



