24 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



In 1896 Cope describes Chilonyx as follows: 



"Teeth compressed, with an apex; no canine; os tabulate produced into a 

 tuberosity or horn; top of head scutate." 



Chilonyx rapidens Cope. (Plate 10, fig. 2.) 



Bolotaurus rapidens Cope, Proc. Am. Phil. Soc., vol. xvil, 1878, p. 507. 

 Chilonyx rapidens Cope, Proc. Am. Phil. Soc., vol. xx, 1883, p. 631. 



Type: A single tooth from the posterior or middle portion of series. No. 4356. 



Paratype: No. 4357 Am. Mus. Nat. Hist. Cope Coll. From Texas. 



Original description: "The size is many times greater than that of the species 

 of this genus (Bolosaurus) already described, and it is uncertain whether the poste- 

 rior tooth possesses the internal ledge characteristic of them. The anterior tooth 

 does not possess it. The transverse diameter of the crown is considerably greater 

 than the anteroposterior, and the convexity of the outer side is without facets. One 

 side of the curve is flatter than the other. The enamel is perfectly smooth. The inner 

 face is occupied by the surface of attrition of the corresponding tooth of the opposite 

 jaw. The supposed anterior tooth is from another locality. Its section is similar 

 to that of the present tooth, and the enamel is similarly smooth. The cutting edges 

 are both smooth, and bounded by a little groove next the plane inner face. The 

 crown is much more elevated than that of the tooth first described, and is in general 

 shaped like a claw. It may be from the pterygoid bone of another genus. 



"Measurements. |. 



"Elevation of the crown (axial) o.oio 



Diameter of crown: 



Anteroposterior 006 



Transverse 008" 



In the "Proceedings of the American Philosophical Society" for 1883, p. 631, 

 Cope gives a characterization as follows: 



"The superior surface of the skull is everywhere flat, as is the external face of 

 the maxillary. The surface of the latter is marked by moderately coarse fossae and 

 grooves, separated by more or less fine irregular but generally longitudinal ridges. 

 The minute sculpture of the superior cranial surface is finer and more punctate 

 in character. The areae of this surface, already mentioned, are arranged as follows: 

 There is a series over the orbits, which are separated from each other by straight 

 grooves, and which grow larger and more swollen posteriorly. Between the supra- 

 orbital rows, the areae of the top of the skull are separated by longitudinal grooves, 

 except immediately between the orbits, where there are some narrow transverse 

 areae. On the supraoccipital region there is a median subtriangular area, and 

 three narrow longitudinal ones on each side of it. External to these, and on 

 the posterior part of the squamosal region, the areae are larger and more swollen. 

 A cluster of three of these lies between the exoccipital bone, and the smooth descend- 

 ing surface of the posterior edge of the squamosal. Of these the one bounding the 

 exoccipital bone is a robust cone, forming a short horn, like that occupying a similar 

 place in the'homed toad, Phrynosoma douglassi. Between the temporal areae, and 

 in front of the supraoccipital areae, on each side of the middle line, there are three 

 longitudinal areae, which are successively narrower externally, the exterior being 

 very narrow. On the frontal region, anterior to the transverse areae, are two wide 

 longitudinal areae. Each nasal bone has a small median area, from which radiate 

 grooves, of which some of the posterior are close together. 



