44 



A much larger tooth, plate IV, fig. 6, an upper right posterior molar of the 1904 collec- 

 tion, compares favourably in size and general proportions with the third molar of Leptacera- 

 therium trigonodon, Osb. and Wort. Its diameters measure, antero-posterior, 31 mm., trans- 

 verse 37 mm. 



ACERATHERIUM OCCIDENTALB (Lcidy). 



Plate IV, fig. 7. 



Rhinoceros occidentalis, Leidy, 1851. Proc. Acad. Nat. Sci. Phila., vol. V. p. 276. 



This species is recorded by Cope (this volume, pt. I) from the Oligocene of the Cypress 

 hills. A number of lower jaw fragments, belonging both to the collection of 1904 and to the 

 earlier collections, apparently represent species distinct from A. mite and A. occidentale,'bnt 

 they are too imperfect for determination. 



An inferior left posterior molar (collection of 1904) evidently belongs to this species. In 

 it the basal cingulum is developed in front and behind but not on the exterior and interior 

 surfaces. Diameters — antero-posterior 32 mm., transverse 21 mm. 



ACBRATHERIUM EXIGUOM, Sp. nOV. 



Plate V, figs. 3, 4 and 5. 



A mandibular symphysis, collected by the writer in Bone coulee, Cypress hills, in 1904, 

 has entirely diff'erent proportions to the symphysis {Ccenopus pumilus, Cope) from the same 

 locality, already referred to A. mite. This specimen consists of almost exactly the same parts 

 of the jaw preserved in the symphysis of C. pumilus, viz., the anterior end of the left ramus, 

 and a short length' of the right ramus united with it so as to show the extent and form of the 

 symphysis. No crowns of teeth are preserved, but in the left ramus the roots of premolars 2 

 and 3 remain. The alveoli for the canine and for one incisor in each ramus are preserved, as 

 well as the alveolus for premolar 2 in the right ramus, and the anterior half of the alveolus 

 for premolar 3 in the left. 



Comparing it with the symphysial specimen of C. pumilus, the following difierences are 

 apparent : — a narrower and longer symphysis, having increased depth behind ; a more rapid 

 deepening of the ramus from in front backward, with a corresponding increase in transverse 

 thickness ; a greater space occupied by the first two premolars ; and very much larger canines 

 as indicated by their alveoli. The greater depth of the ramus beneath the first two premolars 

 is very noticeable. 



In this specimen, belonging to the 1904 collection, the diastema is of about the same 

 length as that of C pumilus. The alveoli for the canines are 8 mm. apart in front, and close 

 together at a lower level are those for two incisors, one on each side of the median line. 

 Premolar 2 was a tooth of fair size with two well separated roots. 



A small species of Acerathere, slightly exceeding A. mite {pumilum) in size, is here 

 represented, to which the name exiguum is given. The jaw is more robust than in A. pumilum, 

 its main characteristics being the contracted and lengthened symphysis and the enlarged 

 canines. 



