20 University of California Piihlications in Zoology [Vol. 21 



frontals where they unite with interorbital ridges. Interorbital re- 

 gion variable, interorbital ridges sometimes coalescing to form single 

 interorbital crest, or these may be separated by a sulcus and appear 

 as ill-defined ridges. Lamboidal ridge moderately developed. Inter- 

 parietal normally subrectangular, its area less than parietal, its 

 posterior border usually evenly convex, and with its lateral extremities 

 squarely truncate. Frontals convex or truncate posteriorly. 



Rostral region elongated, tapering anteriorly, the least depth be- 

 hind incisors greater than width in same region. Nasals long, exceeded 

 by ascending branches of premaxillae, and in very old individuals 

 sometimes extending anteriorly bej^ond plane of incisors. Posterior 

 termination of nasals emarginate, the sides expanding but slightly 

 anterior to middle ; contour spatulate ; as a rule the nasals slope less 

 obliquely forward than in californicus. Opening for anterior nares 

 with vertical diameter normally equal to, but may be greater than, 

 transverse ; plate forming outer wall and continuous with lacrimal 

 bone internally poorly developed, protecting at the most but a small 

 part of anteorbital foramen. Latter variable in outline ; in no. 21727, 

 it is almost subquadrate, though in type skull it is narrow and high, 

 with inferior portion equal to about one-third width of superior 

 portion. 



Occiput uniformly convex, the median depth in all adults available 

 for examination equal to about 56% of greatest width across lamb- 

 doidal ridge of brain-case. Foramen magnum averaging subtriangu- 

 lar, though exhibiting all extremes of variation characteristic of this 

 group. Paroccipital processes heavy, directed more downwards than 

 backwards, closely applied at their extremities to bullae, and with their 

 posterior margins continued upwards to lambdoidal ridge as con- 

 spicuous crests. 



Floor of brain-case not differing from that in californicus in any 

 essential details. Basioccipital possesses well marked median ridge. 

 Width of basioccipital at suture between it and basisphenoid about 

 one-third its median length. Auditory bullae large, approximating 

 those of aestuarinus in size, with region below meatus flattened. 



Palate narrow, with shallow palatine sulci and slightly elevated 

 median ridge. Lateral pits fenestrated. Interpterygoid fossa variable 

 in width, with posterior margin of palate concave, though sides con- 

 verge more sharply medially than in aestuarinus. Posterior palatine 

 foramina large and wide open. Incisive foramina long and narrow, 

 the outer sides nearly parallel throughout their length, and rounded 

 at their ends. 



Zygomata diverging towards front strongly, the central portion 

 expanded, and upper surface of maxillary root normally wider than 

 in californicus. Jugal variable in outline ; may be expanded centrally 

 or be relatively narrow throughout, though usually mortised into 

 maxillary root of zygoma. Zygomatic arches notched at anterior 

 junction with premaxillae. 



Mandible heavy, with rather short diastema. Ridge for masseteres 

 laterales fairly well developed. Coronoid process long, its base broad, 

 its extremity rising above level of condyle and curved backward at 

 tip. Angular process well developed, rather heavy, curved strongly 

 outward, but not extending posteriad beyond plane of condyle. Peri- 



