MONOCLONIUS CRASSUS. 



73 



ton in his collection included representatives of all the elements except the feet, I am convinced 

 that he had in mind material pertaining to more than one individual. Moreover, it does not 

 seem at all unlikely, but, on the other hand, from a study of the material it appears quite 

 probable, that the actual type material described by Cope was of a composite nature and per- 

 tained to two or more individuals. In the following detailed description of the type I shall 

 include only such material as I can positively identify as having been associated by Cope with 

 the type either in his original or subsequent descriptions: 



The skull. — Those parts of the skull preserved and at present identifiable as certainly asso- 

 ciated by Cope with the type consist of the greater portion of the parietals (first described 

 and later figured by Cope as the episternal) and the left frontal. Among the several squamo- 

 sals in the Cope collection from the Judith River beds I am absolutely unable to identify that 

 mentioned by Cope in the passage quoted above ; neither am I able to determine positively that 

 any squamosal in the collection pertains to this species. 



The parietals are preserved almost entire. Their general form is well shown in fig. 75. 

 They are firmly- united along the median line, and may be described as consisting of a straight, 

 broad median portion, somewhat expanded 



in front and presenting throughout the an- -<ssvn -c^P' s 



terior three-fourths of its length a mark- 

 edly convex superior surface supporting 

 three low, rounded, rugose, median promi- 

 nences appearing at intervals of about 75 

 millimeters. The inferior surface of this 

 median bar is concave throughout the 

 anterior one-half of its length, but plane 

 posteriorly. The anterior extremity shows 

 sutural markings, and its inferior portion 

 is more expanded than the superior, both 

 anteriorly and laterally, for articulation 

 with the postfrontals, and perhaps also to 

 some extent laterally with the squamosals. 

 The specimen distinctly shows that the 

 union between these two cranial elements, 

 the parietals and postfrontals, was by 

 overlap and underlap, like the shingles of 

 a roof, the inferior border of the parietals 

 being overlapped by the superior border of 

 the frontals. Such an articulation would 

 permit a continuous growth of the skull to 



an almost indefinite age. Posteriorly this median bar expands laterally, giving rise on 

 either side to two broad bars, which curve first outward, then forward, and at last inward 

 toward the anterior lateral extremity of the median bar, with which, however, it probably 

 never came in actual contact, although its present imperfect condition does not permit this 

 character to be determined with certainty. These lateral parietal bars have an average 

 width of about 10 cm., though they are decidedly more slender anteriorly than posteriorly. 

 They describe about one-half the circumference of an ellipse, and, together with the median 

 bar, they inclose on either side a large parietal foramen, elliptical in outline, perhaps not 

 entirely inclosed anteriorly, with the longer diameter directed antero-posteriorly and having 

 a dimension of about 315 mm., while the shorter transverse diameter is about 220 mm. in 

 length. Posteriorly and medially the parietal border is broadly emarginate, and at a distance 

 of 10 cm. on either side of the median line there is located the first of a series of undulations 

 which continue at intervals all along the periphery of the parietal, decreasing in prominence 

 anteriorly and becoming almost obsolete just before the squamosal suture commences. The 

 squamosal suture occupies the external (anterior) border of the anterior portion of the lateral 



Fig. 75.— Superior view of parietal of type of Monoclonius crassus, No. 

 3998, American Museum of Natural History, sqs, Surface for articu- 

 lation with squamosal; pfs, surface for postfrontal. One-eighth 

 natural size. 



