osborn: OLIGOCENE, MIOCENE, pliocene equid.e. 



Type. — Amer. Mus. 683. Second and third right upper premolars. Measurements: p 2-3 .035. 

 Type figure. — Plate 3.11, text Fig. 35 of this Memoir. 



Characters. — (Osborn, 1904, p. 179, 1918) (1) Type premolars belong to an animal of larger size than the types of 

 M. intermedins, M. validus, or M. gidleyi. (2) Much interrupted transverse crests of the premolars, the cones and conules 

 quite distinct and separate, a character to which the specific name M. crassicuspis refers; (3) internal cingulum strong 

 but not continuous; (4) in the medivallum are low transverse ridges which rise into cuspules in the related species M. 

 annectens; (5) sides of the protoloph and metaloph crenulate as in M. gidleyi; (6) hypostyle a strong transverse crest 

 nearly separated from posterior cingulum ; (7) external cingulum tending to surround parastyle. 



The type teeth were at first mistakenly associated with a pelvis of Colodon (Mesohippus) copei; they are now found 

 to resemble most closely those of Miohippus annectens Marsh from the John Day beds. 



DICERATHERIUM-MIOHIPPUS ZONE. 6. LATE UPPER OLIGOCENE. 



This zone is typified in the Middle John Day of Oregon, which contains large and progressive 

 species of Miohippus. 



Miohippus anceps Marsh, 1874. 



Text Fig. 3(3. 



Anchitherium anceps, sp. nov., Marsh, O. C. "Notice of New Equine Mammals from the Tertiary Formation, 

 Arts (3), Vol. VII, No. 39, Mar. 1874, p. 250. No figure. 



Am. Jour. Sci. and 



Horizon and locality. — " Miocene deposits of Oregon." (?Middle) John 

 Day formation, Diceratherium zone. In the Yale Museum catalogue, "John 

 Day Valley Cove, Ore., T. Condon -collector and donor." "The Cove" is a 

 locality on the John Day River. Most of the material collected from it is 

 Middle John Day. 



Type. — Yale Mus. 11285. (Marsh, 1874, p. 250). Type specimens not 

 designated in type description. (Lull, R. S., letter October 23, 1915): "I can 

 only identify part of this type, consisting of the left maxilla with premolars 

 1-4, the back end of the right mandible with molars 2 and 3, with a gray 

 matrix. Marked ' Anchitherium anceps type.' John Day Valley (Cove) Ore. 

 T. Condon collector and donor. Catalogue number 11285." Measurements: 

 (Marsh, 1874) p 1 " 4 .0475; p 4 a.p. .013, tr. .0155; m 3 a.p. .017, tr. .008. In 

 cotype (second specimen) p L m 3 .082 ; in 1 " 3 .037. 



Type figure — The new type figure (text Fig. 36) represents the first speci- 

 men mentioned in Marsh's description. 



Characters. — (Marsh, p. 250) The author observed that the remains of 

 this species indicate (1) an animal about as large as a sheep. (2) It differs 

 from Mesohippus (A.) bairdii in its larger size. (3) The limbs so far as known 

 are similar to those of Anchitherium. (4) Skull has a large antorbital fossa; 

 (5) skull depressed between the orbits; (6) the antorbital foramen is above 

 the centre of the third premolar; (7) Malar extending farther back below the 

 orbit. (8) Lower teeth agree essentially with those of Anchitherium; (9) ex- 

 ternal cusps of upper molars with stouter buttresses; (10) concavities between 

 them divided by more prominent vertical ridges. (Lull, letter October 23, 

 1915) "Marsh's description of Anchitherium anceps calls for more data than 

 this specimen [Type, Yale Mus. 11285] can furnish. One second skull (green 

 matrix) which could have been seen by him does not tally accurately with his 

 description though I have always supposed it to be .4. anceps. " 

 (Osborn, 1917) From these notes by Lull it appears that the characters of Miohippus anceps rest on the type speci- 

 men. The association of the second specimen (skull) is somewhat doubtful. 



Mioh, 



PP u: 



anceps 



Fig. 36. Type of Miohippus anceps 

 Marsh, Yale Museum 11285, p 1 " 4 of left 

 maxilla, m 2 -3 of right mandible. Natu- 

 ral size. 



