June, 1912. New Titanotheres — Riggs. 35 



In its Uintah representatives Dolichorhinus is one of the most 

 conservative of the titanothere groups. Its greater specialization 

 apparently occurred at an earlier date. The essential characters of 

 the genus are well established in the earliest known representatives. 

 Within its Uintah range there is comparatively little variation between 

 those individuals which may be regarded as in the line of sequence. 



D. longiceps is one of the most common Uintah species. It occurs 

 in relative abundance in the upper half of Horizon A, less frequently in 

 Horizon B. It has a known vertical range of 700 feet. In the lower 

 horizon, in the vicinity of Section 1 (Fig. 1) this species was traced 

 through a vertical series of 400 feet. The several specimens of Doli- 

 chorhinus collected from this locality all belong to one species. They 

 display some variation in size and in structure. The variation in size 

 is indicated by the length of skulls in millimeters (525-560). The 

 smallest skull came from the top of the series, a larger one from near 

 the base. There is a more noticeable variation in the size of canines, 

 breadth of the premaxillary region and of the sagittal area. (See table 

 of measurements.) These differences are evidently due in a great 

 measure to sex. The type specimen described from Horizon B is similar 

 in size to the larger specimens from Horizon A. The premaxillaries 

 are broad, the alveolus indicates larger canines. In the development 

 of horn-cores this species is less advanced than any other of the genus. 

 There is a rounded angle over the eye in the vicinity of the fronto-nasal 

 suture, but in no specimen observed is there a prominent excrescence 

 or rugosity. 



The type specimen of D. cornutus* is a somewhat more highly spe- 

 cialized form than D. longiceps. This specialization appears in the 

 greater breadth of the supra-cranial area, in the more highly developed 

 horn-cores, and the elongation of the cranial, as compared with the 

 facial, region. At the same time there are those elements of similarity 

 between the two which suggest a common stock. The present writer 

 would, therefore, regard the type of D. cornutus as a more advanced stage 

 of the phylum which includes D. longiceps. This appears to be an indi- 

 genous line extending through the greater part of the Lower Uintah series. 



The species D. heterodon and D. fluminalis must be regarded as 

 aberrant forms. The former species as figuredf shows no indication 

 of the backward shifting of the posterior nares so characteristic in 

 other species of the genus. If this figure of the nares is correct the 

 great convexity in the supra-cranial region is the chief distinction 

 between this form and Mesatirhinus superior. The position of the nares 



* Bull. Amer. Mus., Vol. VII, p. 90. 



t Annals Carnegie Mus., Vol. VI, p. 310. 



