96 THE MERYCOIDODONTID^; 



Eporeodon thurstoni Stock 1934 

 PI. XLIII, fig. 1 



Original Reference: On the occurrence of an orcodont skeleton in the Scspe of South Mountain, Calif. 

 Proc. Nat. Acad. Sci., XX, pp. 518-523, pi. 2. 



Type Locality: Willard Canyon, South Mountain, Ventura County, California. 



Geologic Horizon: Upper Oligocene (Sespe). Dominantly maroon-colored shale and siltstone, overlying 

 a stratum of white crossbedded sands at type locality. 



Type: Holotype, Cat. No. 1566 C.I.T., nearly complete skeleton, lying in the slab with the left side 

 cleared of matrix. Named in honor of James E. Thurston. 



Specific Characters: This species approaches E. socialis in size but is somewhat smaller. 

 There is an antorbital pit, and the bulla; are large. The orbit is decidedly large. The skull lacks 

 the greater portion of the cranium, so that it is unwise to diagnose the skull characters until more 

 comparable material is brought to light. 



Skeleton: Stock records the fact that the right pes has a rudimentary element articulated with 

 the navicular and situated above the proximal end of Mt. II. He infers that it may represent a 

 fused entocuneiform and rudimentary Mt. I. Its posterodistal end is rounded. 



Eporeodon trigonocephalus (Cope) 1884 

 PI. VIII, figs. 4-6 



Original Reference: Synopsis of the species of Oreodontida?. Proc. Amer. Philos. Soc, XXI, pp. 514- 

 517 (Eucrotafhus trigonocephalus). 



Type Locality: On the North Fork of the John Day River, Oregon. Referred specimens from Turtle 

 Cove and Bridge Creek, John Day Valley. 



Geologic Horizon: Lower Miocene (upper John Day — light-gray matrix). 



Type: Holotype, Cat. No. 7505 A.M.N.H., skull of an old individual, lacking most of the crowns of the 

 teeth. Collected by C. H. Sternberg. 



Specific Characters: The skull is about the size of that of Merycoidodon culbertsonii and 

 is flat and broad (brachycephalic), with the muzzle somewhat depressed. The maximum expansion 

 of the zygomata is just in advance of the glenoid surface. The malar and the squamosal portion of 

 the arch are about equal in depth, with the latter rising very gently posteriorly. The nasal bones 

 are obtuse posteriorly and gently concave transversely. They do not extend back to the antorbital 

 margin and are nearly uniform in width, except for a gradual decrease near the posterior part. The 

 lacrimal bone has a moderately large pars facialis, with a deep fossa confined entirely to the lacrimal 

 area. The -pars facialis is nearly quadrilateral but slightly deeper than long. The frontals are wide 

 and gently concave transversely and extend slightly anterior to the lacrimal bone. The orbits are 

 large and round and look upward, outward, and forward. The temporal ridges unite at a point 

 just above the anterior edge of the glenoid surfaces to form a high, thin, and prominent sagittal 

 crest, somewhat less than a third of the skull length. The supraoccipital crest is produced beyond 

 the occipital condyles, and the wings are moderately open. The brain case is well developed and 

 has no distinct ridge along the parietosquamosal suture. The U-shaped palatonarial border is 

 located 14 mm. beyond the end of the maxillary bone, and the palate is wide and nearly flat. The 

 basicranial axis is very shallow. The bulls are medium in size, and ovoidal in shape, resembling the 

 form seen in Agriochosrus, with an external ridge enclosing a groove continuous with the stylohyoid 

 fossa, and the long diameter of the bulla; is directed forward and inward. The glenoid articu- 

 lar surfaces are gently convex and are transversely and anteroposteriorly wide. The postglenoid 

 process is of moderate size, and the base is outwardly extended to make the external border decidedly 

 oblique and the apex narrow. The paroccipital process is not separated from the bulla by a marked 

 groove, and the maximum basal diameter extends outward and backward. Index: 0.74. 



