592 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



fouud a corresponding piece of the opposite side of the skull, but with 

 a more extensive attachment of an adjoining bone. I therefore describe 

 this bone in preference to the first named. It consists of two bones, one 

 a tabular mass, the other a projecting body resembling a horn-core, 

 standing on one of the extremities of the table, and at right angles to 

 its plane. The tabular part of the bone is thick, and its free border 

 (opposite to the horn-like bone) is excavated, so as to be double. The 

 two plates are connected by cross pieces, which inclose three fossae. 

 Both the marginal and inferior faces of the bone display smooth sur- 

 faces, as though for synovial articulations. The external surface is 

 roughened with tubercles. The hornlike bone rises from the probably 

 exterior border of the tabular bone, which embraces part of its base in 

 a fixed articulation. It is a rather short and stout cone, with a sub- 

 triangular section, much rounded on the inner side. The apex is rather 

 abruptly contracted from the inner and from what I suppose to be the 

 superior sides. Its base is continuous with that of the tabular bone, and 

 terminates externally, *. e., on the side away from the tabular bone, in 

 a thick projecting rim. The surface of the horn-like portion is deeply 

 grooved and scored, probably for nutritive vessels, as the grooves 

 are continuous. The texture of these bones is for some distance dense, 

 but is more spongy in the center. The corresponding bone of the oppo- 

 site side does not differ from it. (See Figs. 5, 8, 8a. ^ 



These bones are evidently lateral 5 but little can be asserted as to their 

 true nature. The position in which one of them was found would lend 

 support to the view that they are the united opisthotic and squamosal, 

 or either of those bones plus the quadrate. Certain it is that none of 

 those bones are attached suturally to the posterior part of the cranium 

 in this animal, in which it differs from all other Reptiles. The infero- 

 anterior surface of the exoccipital resembles much more that of the same 

 region in Birds, and the proximal faces in the anomalous bones described 

 are of similarly smooth character. One result is certainly derived from 

 this examination, viz, that the Dlnosauria (if this genus belong to that 

 order) do not pertain to the division of BeptiUa with fixed os quadratum. 

 This is a realization of an anticipation published in 1870,* in the'follow- 

 ing words : — " Those {Reptilia) which consolidate the periotic elements 

 but retain the partial freedom of the quadrate, on the other hand, lead 

 to the Avine class. These are the Oniithosauria., and perhaps, when 

 we come to know the cranium, the Dinosauria, At least this may be 

 predicated, if the structure of the foot and ear-bones are correlated in 

 this group as they are elsewhere." It is probable that the horn-like 

 processes were directed forward, and also, if the position in which the 

 attached one was found be normal, in a line extending below that of the 

 sphenoid. This position would relate it to the quadrate. This subject 

 may be considered in connection with the structure of the mandible, 

 discussed farther on. 



* Proceed. Amer. Assoc. Adv. Sci., 1870, p. 23L 



