NO. 1698. A NEW RHYWCHOCEPHALIAN REPTILE— OILMORE. 37 



The position of the incisor in Op-lsthias i^artis at the extreme ante- 

 rior angle of the alveolar border, aside from other differences, would 

 at once distinguish this form from Sphenodon. 



For a distance of 5.5 mm. the incisor is followed by a sharp alveolar 

 border without teeth. Following this edentulous portion, the pre- 

 served teeth are regular, and steadily increase in height from the 

 front toAvard the back, reaching their maximum size in the tooth 

 next to the last, wdiich again diminishes. VieAved from above, the 

 unworn teeth are pyramidal in shape, the anterior face being slightly 

 concave, transversely. 



The larger of the posterior teeth of the series have a single faint, 

 median, vertical depression on both the outer and inner surfaces. 

 Those on the outer surface reach nearly to the apex of the teeth. 



The dental series of the paratype shows but slight evidence of wear, 

 and the anterior edentulous portion is much shorter than in the type 

 specimen. The apices of the anterior teeth of the holotype are much 

 worn, only the two next to the last having the acutely pointed apices 

 of the teeth of the younger individual (Cat. No. 2858), all of which 

 are sharp. The most anterior of the dental series in the paratype are 

 mere denticles barely distinguishable to the naked eye. 



As in Sphenodon^ it appears that as the anterior teeth are worn 

 doAvn, their function is performed by the sharp border of the dentary, 

 and also, as in that genus, the teeth wear down more rapidly in front 

 than behind. 



Discussion. — It is impossible, from so little of the skeleton, to say 

 much of the animal's relationships, but the close resemblance of the 

 specimens just described to the living Sphenodon. (compare fig. 1 

 with fig. 2, pi. 11) would indicate without question their rhyncho- 

 cephalian nature, and therefore they may be very properly assigned 

 to the family Sphenodontida? until more is known of the skeleton. 



On account of the meagerness of the evidence, and washing to avail 

 myself of his wide knowledge of the reptilia, the specimens were 

 submitted to Dr. S. W. Williston, who was generous enough to give 

 me an oj^inion on them. In part he writes me as follows : 



Your rbynchocephalian comes the nearest, I think, of any described form to 

 that described by H. v. Meyer long ago as Homccsaurus from the Solenhoefn 

 beds and the Kimeridge, but no closer than it does to the living SpJicnodon. 

 There can be no doubt, I believe, but that you have in these jaws the first 

 representative in America of a true terrestrial rhynchocephalian. 



Geological horizon. — The deposit from which the specimens dis- 

 cussed in the preceding pages were obtained, was designated by 

 Marsh's collectors as '' Quarry 9." It was from this quarry that most 

 of the Jurassic mammals described by Professor Marsh were found, 

 and on that account the contemporaneous reptilian fauna is of added 

 interest. In 1901 Dr. ¥. B. Loomis published a" stratigraphic sec- 



« Bull. Amer. Mus. Nat. Hist., vol. 14, 1901, pi. 27, fig. 2. 



