87 



ends of the teeth broken off. The alveoli of the two jaws incline at a narrow 

 angle to each other; hence the teeth, which alternate, cross each other near 

 the middles of the crowns. The parts preserved appear to belong to the 

 premaxillary bone, though no suture can be found, and the bony walls are so 

 thin as to render their obliteration a probability. There is a keeled ridge 

 along the middle line above, which is not continued to the margin of the bone. 

 The form of the muzzle is narrow; the sides subparallel-near the tip, which 

 is elongate rounded. The mandibular symphysis, however, is not very elon- 

 gate, as the rami are given off at three inches from the tip. The latter ap- 

 pear to have been quite slender from the various small sections or pieces sent 

 with the muzzle. The premaxillary border of 4 inches 7 lines exhibits eight 

 teeth, or their alveoli, of which the median two are close together, and not sep- 

 arated by any mandibulars. The sections of the teeth are round or oval, and 

 their sizes are irregular, probably on account of differing age and degree of 

 protrusion. The diameters at alveolar margin vary from 6 lines to 3. Their 

 form is slender conic, or, with the root, slender fusiform, and the pulp-cavity 

 is small and median, sometimes cylindric, and sometimes narrowed. The 

 surface, from a short distance above the alveolar margin to the tip, is marked 

 with acute, threadlike ridges, which are sometimes interrupted, and sometimes 

 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 inches 0.05 line; of the muzzle of the 

 seventh tooth, 3 inches 7.5 lines; at the third tooth, 2 inches 4.2 lines. 



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 accident. 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 down- 

 ward ; while, those of the cervical and caudal region being narrower, the 

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



The habits of this species, like that of its known allies, were rapacious, 

 as evinced by the numerous caninelike teeth, and the fish-remains taken 

 from beneath its vertebrae. The general form of this reptile was that of a 

 serpent, with a relatively shorter, more robust, and more posteriorly-placed 



