OSTEOLOGY OF CARNIVOROUS DINOSAURS. 125 



teeth are more triangular than in the other genera of the order; but whether or not this statement had 

 its basis in this specimen is doubtful, inasmuch as the crowns of all the teeth are missing and the roots 

 almost wholly concealed by matrix. This dentary bone (Cat. No. 2315, U.S.N .M.) probably came from 

 the same locality and level as the type of L. lucaris Marsh. 



In 1896 1 Marsh again mentioned this species and presented the same figures. In a footnote on 

 page 163 he remarked that the skull of Allosaurus Jerox had an aperture in the maxillary in front of 

 the antorbital opening. The context appears to indicate that "Allosaurus Jerox" is a slip of the pen 

 for Allosaurus fragilis, just as Labrosaurus Jerox seems to be called Labrosaurus Jragilis on page 270. 

 At any rate, this is the only mention that Marsh made of the skull of either L. Jerox or A. Jragilis. In 

 the definition of the family Labrosauridae 2 he mentioned no part of the skull but the lower jaw. 



On page 270 of the work cited Marsh referred a third species to Labrosaurus — namely, L. sulcatus. 

 This is done in the explanation of plate 13, figure 1; and, so far as the writer is aware, Marsh nowhere 

 else mentioned this species. Three views of a single tooth are given, but there is no description and 

 no statement as to the origin of the specimen. 



Inasmuch as no teeth or parts of the skull were, so far as Marsh informs us, present with the type 

 of L. lucaris, and only teeth or parts of the lower jaw appear to have been represented in the types of 

 the other species, one is at a loss to understand on what grounds the second and third species were 

 referred to Labrosaurus. Furthermore, it may be worth while to inquire whether L. Jerox and L. sulcatus 

 are congeneric. 



The type of L. sulcatus is a tooth which, judging from Marsh's figures, represents a crown 30 mm. 

 high, with a base whose antero-posterior diameter is 12.5 mm. and whose transverse diameter is 12 m. 

 There is a posterior face which appears to have been somewhat concave, its outer boundary being formed 

 by a crenulated, its inner by a smooth, carina. The outer face of the tooth is ornamented at the base 

 by about eight ridges, of which only three remain at the apex. The inner and the posterior faces are 

 represented as being smooth. 



As already stated, the jaw of L. Jerox presented to Marsh little or nothing of the teeth. The crowns 

 of all the functional teeth are missing and the roots were almost wholly concealed by matrix. A section 

 of the base of the crown furthest in front showed above the enveloping sandstone. Of this matrix the 

 writer has removed enough to expose a part of the outer and front faces of the tooth. The inner face 

 had been almost wholly absorbed by the successional tooth, of whose apex about 9 mm. are now laid 

 bare. The functional tooth had an antero-posterior diameter of 15 mm. and a transverse diameter 

 of 9 mm. The later diameter was near the front of the tooth — a fact which indicates that the anterior 

 cutting edge had subsided far above the base of the crown. The hinder edge seems to gave reached 

 the base. The outer and anterior faces and the little that remains of the inner face are wholly smooth. 

 The inner face, too, of the successional tooth is perfectly smooth and both the anterior and posterior 

 cutting edges are crenulated. 



The writer has likewise exposed the tooth which was displacing the sixth functional tooth, the 

 outer wall of whose base still remains. The apex of the successional tooth is broken off. The long 

 diameter at the section thus furnished is 8.5 m.; the short diameter, 5.5 m. The inner and outer 

 faces are equally convex, both are smooth, and both cutting edges are crenulated. 



Such being the structure of the teeth of the types of Labrosaurus Jerox and L. sulcatus, it becomes 

 evident that the two species belong to quite distinct genera and almost certainly to different families; 

 but which of them belongs to Labrosaurus, if either, can be determined only by future discoveries. 



In the lower jaw of L. Jerox there were plainly 12 teeth. The first was placed 63 mm. behind the 

 tip of the jaw, between which and the tooth there is a deep notch. The posterior part of the dentary is 

 bent downward in an extraordinary way, somewhat like that of a fringilline bird. These peculiarities 

 show that this species belongs to a family entirely distinct from that typified by Allosaurus. 



Although I have not had the opportunity of examining the type of Labrosaurus 

 sulcatus Marsh the illustrations lead me to believe that it is a premaxillary tooth. 

 In the event of this suggestion proving correct, the differences noted by Hay between 

 it and a tooth of the dentary of Labrosaurus ferox would form no basis for the con- 



1 Dinosaurs of North America, pp. 163, 270, pi. 13, figs. 2-4. 



* Amer. Journ. Sci., vol. 50, 1895, p. 493 ; Dinosaurs of North America, p. 239. 



