3^8 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



comme reellement acrodont a la maniere de celles de beaucoup de Sau- 

 Kiens actuels." Professor Owen goes on to say, — " The enamel develops 

 a pair of opposite low ridges which are minutely crenate ; the crena- 

 tion becomes abraded at the apical part of used teeth, but is demon- 

 strated in unworn and uuextricated crowns. Many saurians, both 

 Orocodilian and Lacertian, show the creno-bicarinate character, but no 

 Ophidian does." If the characters here mentioned were as universally 

 present in the types to which Professor Owen refers as he seems to sup- 

 pose them to be, they would have less significance than he attaches to 

 them ; but the variety presented by all the orders of reptiles is such as 

 to render the above remarks quite irrelevant. Moreover, the statements 

 are inaccurate. Teeth with two cutting edges are not uncommon in the 

 Ojyhidia (e. g., genus OjiJiiholus, the posterior maxillaries), and are far from 

 universal among Pytlionomorpha. The teeth of Platecarpus are charac- 

 terized by the absence of cutting edges, having a subcircular section.* 

 In CUdasteSj they are not crenate. 



F-ifteenth.— The presence of osseous dermal scuta is cited in evidence 

 of the Lacertilian relationship of the order. Should such scuta have 

 existed, it would not make the MosasauridcB Lacertilians, since they 

 characterize other orders much more generally; but lam safe in saying 

 that such structures had no existence in the known genera of Pythono- 

 •morpha. I have recently received large accessions of material belong- 

 ing to these reptiles in admirable preservation, and have found no 

 dermal bones. I have observed certain osseous segments arranged in 

 lines, whose character I have not yet determined. Their form is rect- 

 angular, their tissue spongy, and their surfaces without sculpture. 



Sixteenth. — The presence of the columella is rightly regarded by Pro- 

 fessor Owen as evidence of Lacertilian relationship. But this character 

 is not a crucial test, since the lizards of the suborder Ehiptoglossa are 

 without it, and the Bhyncliocej^halia and various turtles possess it. 



IV.— CONCLUSIONS. 



I now recur to the propositions which I endeavored in the work 

 already cited t to demonstrate, and which have not been admitted by 

 Pt'ofessor Owen. They are expressed in the following language : — " That 

 these repliles . . . constitute a distinct order of the Streptostylicate 

 group; . . . that they present more points of affinity to the Serpents than 

 ■does any other order." My conclusions that they are not nearly related 

 to the Varanidw, and that the order is nearer to the Lacertilia than to 

 any other, being sustained by Professor Owen, are not further con- 

 sidered. 



As regards the claim of the Mosasauroids to position in an order dis- 

 tinct from LacerfiUa, I do not enumerate a large number of subordinate 

 characters, in which they differ from all known Lacertilia, because such 



~ * Eeport U. S. Geol. Sur. Terrs, ii. p. 141. 



tEeport U. S. Geol. Surv. Terrs, ii. p. 126. 



