with Descriptions of New Genera and Species. 99 



Eporeodon leptacanthus pacificus (Cope) 1884. 



Holotype, No. 7502, Cope Coll., A. M. N. H. Upper Oligocene (middle 

 John Day), John Day and Crooked rivers, Oregon. 



Specific characters. — Skull long and narrow ; lacr^Tnal 

 fossa large and deep; infra-orbital foramen above pos- 

 terior part of P^ ; long sagittal crest ; postorbital con- 

 striction moderately wide; palate moderately produced 

 posteriorly; bulla large and laterally compressed, with 

 a small forward prolongation not seen in any other species 

 of this genus ; bulla separated from postglenoid tubercles, 

 which are oblong and small ; paroccipital process slender 

 and greater diameter transverse to sagittal plane ; pos- 

 terior nares shaped like a shallow open V ; posterior part 

 of nasal bones pointed and extending to anterior margin 

 of orbit. 



At least 50 individuals are .present in this collection 

 from Turtle Cove, Haystack Valley, Bridge Creek, Clarno 

 Bottom, and from 5 or 6 miles below Cottonwood. 



Measurements of Holotype. 



mm. 



Total length of skull 241 



Bizygomatic diameter 137 



Superior molar series, length 47 



Superior premolar series, length 44.7 



Diameter, postorbital constriction 41 



Cat. No. 10143, Y. P. M., is tentatively referred to E. 

 pacificus. This specimen, collected at Turtle Cove in 1875 

 by L. S. Davis, is that of an old individual, probably a 

 male. The major differences from the type of E. paci- 

 ficus are : pterygoid process of the maxilla strongly 

 developed, extending posteriorly and ending in a blunt 

 point; posterior nares semicircular; glenoid articular 

 surface wide and heavy; bullae smaller; mastoid hea^^ 

 and rugose and paramastoid thickened, with its greater 

 diameter oblique to sagittal plane, instead of transverse ; 

 mesocephalic instead of dolichocephalic ; length of molar 

 series 44 mm., premolar, 49, but total length of dental 

 series including canine is the same as that of E. pacificus; 

 anterior zygomatic pedicle heavy, including malar. 



It is probable that both old age and sex have produced 

 these variations from the type. Just what proportion of 



