CROCODILIANS, LIZARDS, AND SNAKES. 543 



uudivided scale. Three folds on the throat, the anterior connectinj^ 

 the ears inferiorly and encircling the head. Pupil vertical ; no eyelids. 

 Digits 5-5. 



Teeth pleurodont, tricuspid; about ten uj)i)er maxillary, nine pala- 

 tine. Roof of mouth extended backward as far as angle of mouth and 

 ending in a W-shaped outline, the central angular notch behind. This 

 is due to dermal flaps extending from the palatine bones, which over- 

 lap on the middle line. Tongue thick, fleshy, depressed, and oval, 

 entirely attached behind and by a central band, the terminal two-fifths 

 free, and slightly notched, the base entire. On the basal third of the 

 tongue above are two obli(iue series of wrinkles converging anteriorly; 

 these soon become finer and closer, the anterior portion being covered 

 with short, compact, depressed, scale-like papillae 



Osteologi/. — iMy knowledge of the osteology of this genns is derived 

 from the X. rivers i((n<(, specimens of which I owe to my friend, Br. J. J. 

 Rivers, of Oakland, California. 



The premaxillary has an elongate spine above and a nearly trans- 

 verse posterior border below. Nasals well developed, distinct. Frontal 

 single, grooved below. Parietal single, without pineal foramen, pro- 

 duced posteriorly so as to overhang the occipital bone and foramen 

 magnum, being connected with the former by a median keel, which it 

 sends downward. The supraoccipital is siibhorizontal and is not 

 articulated in the usual way with the parietal, having only the median 

 contact above mentioned. It is coossified with the exoccipitals. The 

 prefrontal is small and is not produced far over the orbit. Lachrymal 

 absent. Jugal with the superposterior limb expanded. Postfrontal 

 and postorbital fused into a triangular bone, which bounds the parietal 

 externally, thus, with the supratemporal, roofing over the temporal 

 fossa. Supratemporal in contact throughout with tlie j^arietal, except 

 where separated by the narrow splint of a paroccipital. Quadrate with 

 one, a large external conch. Vomers closely juxtaposed throughout, 

 coossified anteriorly, the median portion of the two elements with an 

 excavation. Narial orifices nearly closed, except posteriorly, where the 

 vomerine process of the palatine overarches them. The latter are in 

 contact in front, but soon spread apart. Maxillary processes rather 

 shorter than vomerine, depressed below them. Pterygoids narrow 

 throughout, not wider than palatines, their posterior part with a groove 

 which looks upward and inward. Basi])terygoids overlapping their 

 entire internal face. Ectopterygoids wide, reducing the palatine fora- 

 men to a mere' slit; with a considerable contact with the palatine, and 

 a recurved portion in contact with the extremity of the maxillary; the 

 internal extremity depressed. No presphenoid; sphenoid separated by 

 suture from basioccipital, whose lateral processes are com])ressed and 

 decurved. The postoptic bone seems to be wanting. The petrosal is 

 well produced beyond the semicircular canal, and is equally jjroduced 

 below the trigeminal foramen, where it Joins a backward directed i)roc- 

 ess of the basipterygoid. The groove below it is well delined and looks 



