CHASMOSAURUS BBLL1 93 



Vs further representatives of this species, 1 would add the companion skeleton, No. 2280 

 C. (PI. XIV, B) 5 skull No. 54(12 A. M.N. II. (PI. VI); and No. 2016 Y.l/.M. The skull of 

 \ 2280, at Ottawa, differs in having a deepU emarginate posterior bar which hears two more 

 epoccipitals on either side of the midline. The orbit is more nearly circular, with the long axis 

 more nearly vertical and the brow horns, especially the left, somewhat recurved. Skull No. 5402 

 A. M.N.H. conforms, except that the brow horns slope forward and are somewhat more anteriorly 

 placed with relation to the orbit than in the type. The rear of the crest is not emarginate, and has 

 four epoccipitals. The Yale specimen also agrees, except that the brow horns are rudimentary, being 

 merely rugose areas above the orbit. 



There is in the American Museum collection the partial skull of a chasmosaur, No. 5656 

 A.M.N. H., collected by C. H. Sternberg in 1917, from the Belly River horizon of Sand Creek, 

 Red Deer River, Alberta. The upper surface of the cranium, including the horns, and the muzzle 

 have been eroded away, but the crest is in a remarkable state of preservation. The specimen is that 

 of a young individual, about 80 per cent grown, with clearly defined sutures and with apparently 

 all of the epoccipitals preserved in situ. 



The outstanding features of this skull are the deeply emarginate posterior bar, bearing two 

 large, sharply pointed epoccipitals on either side of the reentrant curve, together with a marked 

 prominence just behind the terminus of the squamosal which does not at present bear an epoccipital, 

 although in the position of the largest of these in an adult chasmosaur. The parietals have the 

 usual overlapping suture on the outer border of the very large fenestrae just within the squamosal. 

 The latter bone is very short for Chasmosaurus, extending for about two-thirds the length of the 

 parietal. The squamosals are deeply concave transversely as seen from above and bear a longi- 

 tudinal row of boss-like prominences. There are four distinctly sutured epoccipitals at this stage of 

 growth on either squamosal, and the antero-external angle is acuminate. The outer end of the jugal 

 is rounded, with no evidence of an epijugal. Vascular impressions are absent except on the posterior 

 bar of the parietals and on the epoccipitals. This crest resembles most nearly that of No. 2280 in 

 the Ottawa group (PI. XIV, B), the main distinctions, other than size, being the presence of the row 

 of bosses on the squamosal, its somewhat less relative length (although it is still short in No. 2280 as 

 compared with the Chasmosaurus belli plesiotype, No. 2245), four as compared with six squamosal 

 epoccipitals, and the absence of the large epoccipital just behind the terminus of the squamosal. 



In these two animals the differences may be due entirely to age, for it is conceivable that the 

 epoccipitals might increase in number with the lengthening of the bones bearing them. Hence, the 

 two specimens seem without question to be conspecific. The deeply emarginate crest with its four 

 to six epoccipitals and the shorter squamosals may prove to be specific characters, distinguishing 

 this form from No. 2245, the Chasmosaurus belli plesiotype, in which the crest is not emarginate 

 and the squamosals are relatively long. On the other hand, these may be sex differences. This 

 would accord with the idea of C. M. Sternberg'" who thinks that No. 2245 may have been a male 

 and No. 2280 a female on the ground that, "it is common, among reptiles, for the female to be 

 larger than the male," No. 2280 being somewhat the more robust. I have referred the question of 

 the relative size of the sexes in reptiles to Raymond Ditmars whose authority no one will question. 

 He writes as follows:*" "I have found, with the greater number of snakes, that the females are 

 larger and heavier than the males. With some species, this is so marked that the sexes can be 

 distinguished at a glance. 



"Among the lizards, however, the reverse is generally the case. In fact, it may be fairly sate 

 to say that with the majority of the species, the males are a bit larger and certainly more ornate." 



It would seem that the analogy lies with the lizards if anywhere, so that on two counts the 

 specimen with greater robustness and greater ornamentation at the rear of the crest (No. 2280) 

 should be considered the male. It is unfortunate that the muzzle and nasal horn, as well as the 

 distal end of the ischium, cannot be contrasted, for these elements, lacking in one or the other animal, 

 were restored from the one possessing them. 



-ternberg, C. M., 1927, B, p. 67. 

 letter of October 22, 1932. 



