92 THE CERATOPSIA 



Genus CHASMOSAURUS Lambe 



The type of this genus, No. 491 G.S.C., is a portion of the crest consisting of the median bar 

 and part of the posterior transverse bar, first described by Lambe 2 ' as Monoclonius belli. Because 

 of Lambe's conviction that this genus was directly ancestral to the Lance genus Torosaurus, the 

 name Protorosaurus was given to it in 191 4, 28 together with a detailed description based upon the 

 plesiotype, which supplied all the necessary details except the anterior part of the skull, including 

 the muzzle and nasal horn. The first of these I find to be important in Chasmosaurus, the second 

 rather less so, although a principal diagnostic character in other genera. Later in the same year, 20 

 a further description of this species was given, with the new generic name, Chasmosaurus, replacing 

 Protorosaurus, which was found to be preoccupied by H. v. Meyer for a genus of Permian reptiles. 



The generic characters, as given by Lambe, 29 are as follows: "Skull large, broadly triangular 

 in superior aspect, with a narrow, abbreviated facial portion, and a broad and greatly expanded 

 posterior crest ending squarely behind. Coalesced parietals forming a slender framework enclosing 

 large sub-triangular fontanelles. Squamosals very long and narrow with a scalloped free border. 

 Epoccipitals present. Supraorbital horn-cores small, upright. Supratemporal fossae of moderate 

 size. Postfrontal fontanelle present. Jaws robust. Teeth large, of the ceratopsian type. Body 

 covered with non-imbricating, small plate-like, and smaller tubercle-like scales." 



The holotype of this genus, incomplete as it is, shows no specific characters; but, as in Mono- 

 clonius and Centrosaurus, serves only to establish the genus. The plesiotype, on the other hand, 

 allows for an almost complete generic description and establishes the species belli as well. In spite 

 of the fact that the various skulls show considerable variation among themselves, two other species 

 seem to be definable, although in each instance based upon a single skull. 



The contrasting specific characters lie in the brow horns, whether longer or shorter than the 

 nasal horn, the former being the more progressive condition. The muzzle, whether long or short, 

 seems also to be distinctive. The emargination of the posterior bar of the crest may prove to be 

 distinctive; at present, it seems to be merely an individual, or possibly a sexual variation. On the 

 basis of these and certain minor distinctions, the following species may be defined. 



Chasmosaurus belli Lambe 30 

 PI. VI, XIV, Bj Text Fig. 30 



Holotype: No. 491 G.S.C.; parietal. 



Horizon: Belly River. Upper (primitive mammal) beds. 



Locality: On the east side of Red Deer River, below the mouth of Berry Creek, Alberta. 



Collector: L. M. Lambe, 1898. 



Plesiotype: No. 2245 G.S.C. (PI. XIV, B), consisting of a large part of the skull and skeleton now mounted at 



Ottawa. 

 Horizon: Belly River formation. 



Locality: On the east side of Red Deer River, a short distance below the mouth of Berry Creek. 

 Collector: C. H. Sternberg, 1913. 



The distinctive characters of this species are as follows: Brow horns short, trihedral, and 

 erect; orbit elliptical, with long axis nearly horizontal; posterior bar of crest not emarginate — large 

 epoccipitals are present at the outer rear corners of the crest just behind the termination of the 

 squamosal, but there is none borne on the parietals; squamosals bearing seven or eight epoccipitals, 

 increasing progressively in size from front to rear. To these features, determinable from the plesio- 

 type, may be added : Nasal horn larger than the brow horns, although short and robust ; and muzzle 

 long and slender. 



27 Lambe, L. M., 1902, pp. 66-67, PI. xx, Figs. 1, 2, Text Fig. 20. 



28 Lambe, L. M., 1914, A, pp. 131-132. 



29 Lambe, L. M., 1914, B, pp. 149-15 5. 



30 Lambe, L. M., 1902, pp. 66-67. 



