CYCLOPIDIUS 243 



Specific Characters: This is the smallest known species with a short face. The facial 

 vacuities are large, and the nasal bones are narrow, expanding at the contact with the maxillary. 

 Owing to the small portion of the skull extant and to some crushing, very few diagnostic characters 

 can be clearly defined. We can, however, gain much information from the dentition. The palate is 

 relatively wide and but little vaulted. 



Mandible: The horizontal ramus is relatively deep. The symphysis is quite short and straight, 

 with a symphysiodental angle of about 60°. The masseteric fossa reaches forward to a point below 

 the posterior part of M 3 . 



Foramina: The infraorbitals lie above the anterior part of P 4 . 



Dentition: This is hypsodont and crowded. Superior: The canines are relatively long, 

 slender, and slightly recurved. The anterior premolars overlap in both jaws, p 1 ' 2 ' 3 have their 

 anterior parts reduced and appear to be set obliquely in the jaw, especially as their cutting surfaces 

 are directed inward and forward. In M 1 and M 2 the parastyle and mesostyle are much less devel- 

 oped than normal in Cyclopidius and the external surfaces of the paracones and metacones appear 

 flatter. Inferior: The incisors are lacking, as in the superior series, but they must have been minute, 

 judging from the alveolar border. Pi is much larger than P 2 , and the cutting edge of both is set at 

 approximately 45° from the main line of the teeth. There is no diastema between Pi and P 2 , and all 

 the premolars are very much crowded, so that the combined length of the last three is equal to the 

 length of M 3 . The posterior parts of the last three premolars are well developed. In P 3 a slight 

 fold is present on the anterior crescent. The lingual surface of M 3 is somewhat flatter than normal, 

 without a perceptible ridge from the metaconid. The metastylid is about normally developed. 



Discussion: Stock proposed to place this species in a new subgenus, Sespia. It is mainly a 

 matter of personal opinion as to what characters and their degree of importance in any group con- 

 stitute sufficient grounds for erecting genera and subgenera. With the exception of certain tooth 

 variations, his subgeneric characters all fall into the genus Cyclopidius. The feeble development, or 

 absence, of the normal styles on the molars is, in my opinion, a specific character. The lower 

 molars are more nearly like those of Cyclopidius than are the upper in this respect, the latter rather 

 resembling those of Leptauchenia. Stock stated that possibly Sespia represented an early division 

 of the Leptauchenia group tending toward Cyclopidius. My opinion is that C. calif ornicus is not so 

 primitive as Stock thought. It is markedly hypsodont and has a short face, large facial vacuities, 

 crowded premolars, and so on, all characters of the advanced Cyclopidius stage, while the diminutive 

 size and feeble styles on the molars may also be progressive or may be a phase of the evolution of 

 this group that is local in California. We do not know any other Leptauchenia-Cyclopidius repre- 

 sentative west of the eastern part of Wyoming and central Montana, and what evolutionary changes 

 may have taken place and in what directions during the long trek to California can only be surmised. 

 Again, this form may have evolved independently from the transmontane merycoidodont group, 

 possibly from the Eporeodon stock, as we know that Eporeodon and Promerycochcerus were present 

 in both Oregon and California. 



Cyclopidius densus (Loomis) 1925 

 Figs. 170-172; PI. XLIX 



Original Reference: Leptauchenia and Cyclopidius. Amer. Jour. Sci. (5), IX, pp. 245-247, figs. 3-4 

 (Leptauchenia densa). 



Type Localities: Muddy Creek, 25 miles south of Torrington, Wyoming (HT); 200 yards west of 

 Redington, Morrill County, Nebraska (PLT). 



Geologic Horizon: Lower Miocene (lower Rosebud). 



Types: Holotype, Cat. No. 22-595 A.M., nearly complete skeleton, including skull and jaws. Plesiotype, 

 Cat. No. 1-28-8-31 SP, N.S.M., well-preserved skull and jaws. 



Specific Characters: The skull is intermediate in size between C. shnus and C. lullianus 

 and resembles each in certain other characters. The expansion of the zygoma is greatest just in 



