PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 60. 



The skull of Saniwa^ as may well be inferred from the close re- 

 semblance of the various elements to those of the Varanus, had the 

 same light, open construction as in that genus. The similarity of 

 many of the individual bones is remarkable, especially when the 

 Eocene age of the fossil is taken into consideration. 



A skeleton of Varanus salvator (Cat. No. 29551, U.S.N.M.), having 

 a skull of practically the same dimensions as the type of Saniwa 

 ensidens Leidy, has a greatest length of (473 mm.) 4 feet 10 inches. 

 I am of the opinion that the length of the complete skeleton of the 

 fossil specimen would be somewhat less, because of the slightly 

 smaller and shorter vertebrae, but it would certainly have exceeded 

 4 feet in length. Some of the extinct American species as Saniwa 

 major Leidy or Thinosaurus grandis Marsh probably rivaled the 

 largest of the existing Monitors {Varanus salvator)^ which often 



QuJ 



Fig. 1. — Skull of Varanus niloticus. Col, Columella ; Exo, exoccipital ; Fr, fkontal ; 

 Ju, jucjAL ; La, lachrymal ; Mx, maxillary ; N, external nares ; Na, nasal ; Pa, 

 parietal; pi, palatine; Pmx, premaxillary ; Prf, prefrontal; Pro, prootic ; Pt, 

 pterygoid ; Ptf, postfrontal + pcstorp-ital ; Qu, quadrate ; Qnj, quadratojugal ; iSf, 

 supratem-oral fossa ; So, supraoccipital ; Sq, squamosal ; T, ectopterygoid ; Y, 

 supraorbital. (After Cuviek.) 



attains a length of 7 feet. The largest of the American species, how- 

 ever, are small as compared with the Megalania prisca from the 

 Pleistocene of Australia with an estimated - length of 30 feet for the 

 entire animal. 



Basioccipital—The basioccipital is perfectly preserved, except for 

 the loss of its posterior median portion, which with the exoccipitals 

 forms the occipital condyle. It thus forms the median boundary 

 of the base of the foramen magnum, and ventrally is continuous 

 laterally with the exoccipitals. which, as in Varanus, develop thin 

 winglike plates that extend forward in a horizontal plane from the 

 ventral sides of the proximal ends. The anterior, transversely 

 broad, wedge-shaped end is received in a corresponding transverse 

 depression on the posterior end of the basisphenoid. The dorsal 

 surface of the basioccipital is medially depressed, forming a wide 

 longitudinal valley. 



» Lydekker. R. Cat. of Fossil Reptilia and Amphibia, Pt. L, 1888, p. 284. 



