344 Marsh — Restorations of Claosaurus and Ceratosaurus. 



Claosaurus, Marsh, 1890.* 



The most important feature in the restoration of Claosaurus 

 annectens given on Plate VI is the skull, which will be fully 

 described elsewhere, but its main features may be noticed here. 

 This skull is long and narrow, with the facial portion especially 

 produced. The anterior part is only moderately expanded 

 transversely, thus differing from that of Hadrosaurus 

 (Diclonius), a nearly allied form. Seen from the side, the 

 skull of Claosaurus shows a blunt, rugose muzzle, formed 

 above by the premaxillary and below by the predentary, both 

 probably covered in life with a thick, corneous integument. 



Behind the upper part of this muzzle is an enormous lateral 

 cavity, which includes the narial orifice, but was evidently occu- 

 pied in life mainly by a nasal gland, somewhat like that in the 

 existing Monitor, and also seen in some Birds. This cavity is 

 bounded externally by the nasal bone and the premaxillary. 

 The orbit is very large, and subtriangular in outline. It is 

 formed above by the prefrontal, frontal, and postfrontal, and 

 below mainly by the jugal. There are no supra-orbital bones. 

 A distinct lachrymal forms a portion of the anterior border. 

 The infra-temporal fossa is large, and bounded below by the 

 jugal. There is a thin quadrato-jugal between the jugal and 

 quadrate. The occipital condyle is directed backward and 

 downward. 



The nasals are very long and slender, and in front are 

 separated by the narrow superior processes of the premax- 

 illaries. The frontals are short and broad, and somewhat 

 concave above. The parietals are firmly coossified, and very 

 small, forming a thin partition between the supra-temporal 

 fossae. The latter are bounded posteriorly by the massive 

 squamosals, which contain a deep cavity for the head of the 

 quadrate, and also overlap the exoccipitals. 



The striking features of the lower jaw are the massive, 

 rugose predentary, the large and powerful dentary bone with 

 its robust coronoid process, and the very small angular and 

 articular bones. 



The teeth are confined entirely to the maxillary and dentary 

 bones. They closely resemble those of Hadrosaurus, are 

 arranged in the same manner, and appear to be equally 

 numerous.f They were well adapted to a diet of soft succulent 

 vegetation. 



*This Journal, vol. xxxix. p. 423, May, 1890; vol. xliii, p. 453, May, 1892; 

 and vol. xliv, p. 171, August, 1892. 



f The description given by Cope of the skull of Hadrosaurus (Didonius) mirab- 

 ilis, Leidy, is erroneous in various important points. Among the more serious 

 errors are the following : the predentary bone is mistaken for the dentary, the 

 dentary is regarded as the surangular and as the spleuial, while the squamosal is 

 called the parietal. See Proc. Phil. Acad., 1883, p. 97, plates iv-vii. 



