54 



THE EXTINCT BATRACHIA, REPTILIA 



Fig. 12. 



sometimes cylindric, and somtimes nan-owed. The surface from a short distance ahove the alveolar margins to the 

 tip, is marked with acute thread-like ridges, which are sometimes interrupted, and some- 

 times furnished with short branchlets. They are more or less undulate, and do not unite, 

 but simply cease as the tip of the tooth is approached. The latter is smooth without lateral 

 cutting edges. The width of the mandible at the commencement of the rami is 3 in. .05 

 lin. ; of the muzzle of the seventh tooth 3 in. 7.5 lin. ; at the third tooth 2 in. 4.2 lin. 



General Remarks. — The tail is a powerful swimming organ, more or less compressed in 

 life, hence the specific name, which means flat-tailed. 



The danger of injury to which such an excessively elongate neck has been exposed, would 

 render the recovery of a perfect specimen like the present, an unusual chance. The neural 

 spines of the dorsal region are so elevated and closely placed as to allow of little or no vertical 

 motion of the column downwards, while those of the cervical and caudal region being nar- 

 rower, the elevation of the head is quite possible, and an upward flexure easy. 



The habit of this species, like that of its nearest known allies, was raptorial, as evinced 

 by the numerous canine-like teeth, and the fish remains taken from beneath its vertebra?. 



The general form of this reptile, whether it was furnished with large posterior limbs or 

 not, was that of a serpent with a relatively shorter, more robust and more posteriorly placed 

 body than is characteristic of ti-ue serpents, and with two pairs of limbs or paddles. It pro- 

 gressed by the strokes of its paddles, assisted by its powerful and oar-like tail. The body 

 was steadied by the elevated keel of the median dorsal line, formed by the broad, high neural 

 spines. The snake-like neck was raised high in the air, or depressed at the will of the animal, 

 now arched swan-like preparatory to a plunge after a fish, now stretched in repose on the 

 water or deflexed in exploring the depths below. 



Differences from other Sauropterygia. — The only genus with which it is necessary to com- 

 pare this present one is Chnoliasaurus. The following may be noted as generic distinctions: The 

 series of cervicals rapidly diminishes in Cimoliasaurus in absolute size and in relative length of the vertebra?, 

 which are not compressed. In the present genus they maintain a similar length for a considerable distance, 

 diminish in length very gradually and are much compressed. The diapophyses of the dorsal vertebra?, 

 as they descend, in Cimoliasaurus, continue well developed until they attain the inferior planes of the 

 centrum, and have there a downward direction. In Elasmosaurus they cease while yet on the middle of 

 the centrum, and are replaced by pits throughout the remainder of the length. 

 The neural canal is everywhere markedly larger in Cimoliasaurus. 



As the characters of lesser significance may be added, that in Cimoliasaurus magnus the dorsals 

 with elevated diapophyses are considerably larger in the centra than those in which they are situated 

 lower down. In E. platyurus these vertebra? are of relatively equal length. 



The cervical pleurapophyses in C. magnus are anteriorly considerably stouter and less flattened- the 

 same applies to more anterior vertebra?, where they are flatter in both. 



In comparing this species with the Cimoliasaurus grandis, Leidy, from Arkansas, we observe first 

 the generic character of the strong inferior diapophyses in the latter. That species marks itself also 

 as a preeminently short-necked form, as these anterior dorsals are even shorter than in C. magnus, beinn- nearly twice 

 as wide as long. The depth of the articular faces is also relatively greater than in the E. platyurus. 



History. — The determination of the extremities of this species was rendered difficult from the fact that Leidy in 

 his descriptions of Cimoliasaurus, reverses the relations of the vertebra?, viewing the cervicals as caudals and lum- 

 bars, and describing the caudals as belonging to another genus. Not suspecting this error, I arranged the skeleton of 

 Elasmosaurus with the same relation of extremities, and the more wiflingly as the distal cervicals present an extraor- 

 dinary attenuation, even for this type, and also as the discoverer assured me that the fragments of cranium were 

 found at the extremity which is properly the caudal. Viewed in this light many details of the structure were the re- 



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