SYSTEMATIC REVISION 



51 



Fig. 9. 



A. T. Uxensis. No. 4719 Am. Mus. X i. 



B. Restoration of skull. Lettering as usual. 



XK. 



Genus TERSOMIUS Case. 

 Tersomlus texensis Case. 

 Bull. Am. Mus. Nat. Hist., vol. xxviii, Art. xvii, 19 10, p. 180. 



Type: A skull. No. 4719 Am. Mus. Nat. Hist. From Texas. 



Original descri-ption: "The skull is flattened, having nowhere near so 

 much of an arch as in the specimen 

 described by Cope as Trimerorhachis 

 conangulus. The orbits are large, 

 extending so close to the edge that 

 there is a very thin maxillary border. 

 The nares are small and look almost 

 directly upward. The teeth are small 

 and sharply conical with no enlarged 

 ones visible in the maxillary or the 

 mandible. The position and relations 

 of the various bones are shown in the 

 figure. There is no tabulare visible 

 and it is probable that it was not 

 present. Compared with Trimero- 

 rhachis conangulus, which it most resembles, there is no second prosquamosal 

 (intertemporale) and the orbits are much larger and placed farther to the rear. 



MM 



" Length on the median line 32 



Length of the lower jaw 34- S 



Width at the back of the skull 25 



Interorbital width 7" 



Revised description: No change from the original. 



Family DISSORHOPHlDyE Williston. 

 Bull. Geol. Soc. Am., vol. 21, 1910, p. 277. 



Original description: The following summary of the Dissorhophidce and 

 the genera Dissorhophus and Cacops is given by Williston: 



"General characteristics: Skull with the otic notch completely inclosed 

 to form a large ear cavity. Palate with but two large teeth on each side, 

 one at the anterior inner margin of the nares, the other at the posterior mar- 

 gin; mandibular and maxillary teeth of nearly equal size. Parasphenoid 

 reduced. Twenty-one presacral vertebrce; two sacral vertebra; tail short. A dor- 

 sal carapace, composed of lateral expansions of the spines of the vertebrae, with 

 overlying intercalated dermal plates. Cleithrum very large and expanded 

 above. Clavicles small, without exterior pittings. Interclavicle smooth on 

 the dermal surface, small, with a short posterior process. Humerus without 

 ectepicondylar process. Femur with strong adductor crest. 



"Genus Dissorophus Cope: Dermal carapace extending the full width 

 of the body, with a broad and elongated shield in front, covering several 

 vertebrse. Cleithrum less expanded and thicker. Scapula much expanded 

 antero-posteriorly below. 



"Genus Cacops Williston: Dermal carapace but little wider than the 

 vertebrae, narrowed in front and not fused into an anterior shield. Clei- 

 thrum thin and more expanded. Scapula less expanded below, the inter- 

 clavicles and clavicles more slender." 



