ART. 23. 



AN EXTINCT VARANID LIZARD GILMORE. 



19 



ITiG. 17. — Anteuior cau- 

 dal VERTEBRAE OF Sa- 

 NIWA ENSIDENS LEIDY. 



Type, Cat. No. 2185, 

 U.S.N.M. Natural 

 SIZE. Viewed from 



LEFT SIDE. h, UTPO 

 PHYSIS FOR ARTICULA- 

 TION OF CHEVRON ; t, 

 TRANSVERSE PROCESS ; 

 Z' , POSTERIOR ZYGAPO- 

 PHYSIS. 



two flattened forwardly projecting processes between which on the 

 median line is a broad notch. I regard these processes as rudi- 

 mentary zygosphenes (see zg, fig. 15). Marsh ^ notes a simihir 

 articulation on the dorsal vertebrae of Thinosaurus paucidens. The 

 absence of zygantry, however, shows that they 

 no longer function as a true zygosphene-zygan- 

 trum articulation. The posterior half of the 

 upper surfaces of the neural arch is convex 

 and expands outward at its back part to form 

 the posterior zygapophyses (see fig. 14, B), 

 the articular surface of which looks downward 

 and outward. The median part of the arch 

 develops a wide (anteroposterior) spine of 

 moderate height. This spine is very thin, but 

 thickens posteriorly, especially its posterior 

 upper extremity. The posterior part of the 

 arch, including the zygapophyses, overhangs 

 the centrum, but terminates forward of its 

 most posterior extension. 



Caudal vertebrae. — There are 13 caudal vertebrae present, all ap- 

 parently from the proximal fourth of the tail. These are in three 

 blocks of matrix, of which the better-preserved vertebrae, four in 

 number, remain articulated (see pi. 3, fig. 1). These, however, 

 indicate one important difference when compared with the tail of 

 Varanus and that is the low, broad, spinous processes of the presacral 

 region continue back much further in the 

 caudal series. Though they do gradually in- 

 crease in height posteriorly, it appears very 

 doubtful if they ever attained the great height 

 found in the living Monitor, Varatius salvator 

 (see fig.- 17). Nor do any of the 13 vertebrae 

 indicate a fore-and-aft narrowing of this proc- 

 ess such as begins to take place in the third 

 vertebra back of the sacrum in Varanus. 

 The caudal centra are more elongate than in 

 the mid dorsal region; the middle ventral 

 surface is traversed longitudinally by a shal- 

 low depression. They retain the cujD-and-ball articulation found in 

 the presacral series. On the posterior third of the ventral surface 

 of the centrum a pair of short articular protuberances indicate the 

 point of attachment for the chevron (see fig. 18). 



The apparent absence of caudal vertebrae, having high spinous 

 processes, suggests that Saniwa was a terrestrial form having a 



Fig. 18. — Anterior cau- 

 dal vertj;bra of Sa- 

 niwa ENSIDENS LeIDY. 



Type, Cat. No. 2185. 

 U.S.N.M. Natural 

 SIZE. Ventral view. 

 ch, hypophysis for 



chevron ; *, TRANS- 

 VERSE PROCESS. 



' Amer^ Journ. Sci., ser. 3, vol. 3, 1872, p. 299. 



