MESOHIPPUS. 



17 



Mesohippus exoletus Cope, 1874. Spec, indet. 



Anchitherium exoletum, Cope, spec, nov., Cope, E. D. "Report on the Vertebrate Paleontology of Colorado," Ann. Rept. U. S. 

 Geol. and Geogr. Surr. Terr. cmbr. Colorado (for the year 1873), Washington, 1874, p. 496. No figure. 



Horizon and locality. — "Miocene of Colorado" (Cope). Cedar Creek, Logan County, Colorado. Collected by E. D. 

 Cope, IS 73. 



Type. — This type specimen has not been found in the Cope Collection. "Established on a portion of the right 

 maxillary bone, which contains the last premolar and first premolar in perfect preservation and part of the third premolar." 

 Measurements: "Length of fourth and fifth molars .0275, length of fourth molar .0140, width of fourth molar .0125, 

 elevation of fourth molar .0080, length from front of malar to foramen infraorbitalc anterius .0140." 



Type figure. — Xo figure, as type has been lost. 



Characters. — (Cope, 1874, p. 496) "....II. Anterior median tubercle well separated from inner: ....no inner 

 basal lobes; crescents with concave outer faces. . . .These teeth differ from the corresponding teeth in A. bairdii in many 

 respects, resembling in the constitution of their outer lobes some of the symborodonts. The outer faces of these are uni- 

 formly concave to near the shoulder, leaving a very narrow basal ridge and no longitudinal median ridges. The intercre- 

 scentic ridge is incurved and not straight. The anterior middle tubercle is separated from the inner by a deep fissure and 

 grooves to the base; the median is, on the other hand, continuous with the posterior inner. The posterior median is very 

 small. The anterior and posterior basal ridges are small, and there is no trace of basal tubercle between the two medians. 

 Enamel smooth. The size of this animal was probably that of the A. bairdii, but the molar teeth have the antero-posterior 

 diameter greater in proportion to the transverse than in that species. The foramen infraorbitale exterius is over the front 

 of the fourth premolar; it is above the front of the third in A. bairdii." 



The species is indeterminate. No specimen has been found in the American Museum Cope Collection agreeing with 

 Cope's description. 



Mesohippus cuneatus Cope, 1873. Spec, indet. 



Anchitherium cuneatum sp. nov., Cope, E. D. "Third Notice of Extinct Vertebrata from the Tertiary of the Plains." Palceonlo- 

 logical Bull. No. 16, privately printed, Aug. 20, 1873, 8 pp. (p. 7). No figure. 



Horizon and locality. — Head of Cedar Creek, Logan County, Colorado. Probably from the Oreodon zone. Collected 

 by E. D. Cope, 1873. 



Type. — Am. Mus. Cope Coll. 6293. The type and cotype specimens are : upper jaws, milk teeth, dp 2-4 , badly damaged, 

 upper jaws (?) dp 3 , m 1 Am. Mus. Cope Coll. 6296; (?) dp 4 , m 1 Amer. Mus. Cope Collection 6285 are indeterminate (Mat- 

 thew, 1915). Measurements: (Cope, 1873) No. 1 [type], "Length of M.2 and 3 .0260, length of M.l .0130, width of M.l 

 0110; No. 2 [cotype], length of Ms. 1-4 .0410, length of M.2 .0115, width of M.2 .0130." 



Type figure. — These types could not be identified when Cope's Colorado collection was catalogued by W. D. Matthew. 

 As the type is probably lost or misplaced and there is no figure the species must be regarded as indeterminate. 



Characters. — (Cope, 1873, p. 7) "Represented by the superior molar teeth of several individuals one-third smaller 

 than those of the A. [Mesohippus] bairdii. The prominent peculiarity consists in the anterior production of the anterior 

 external cusp anteriorly, giving a wedge-shaped outline to that part of the tooth. The first premolar is quite small. The 

 fore and aft cingula are well developed, and the basal parts of the transverse ridges are partially separated into tubercles, 

 the posterior one sending a low ridge backwards." 



Species Attributed to Middle Oreodon ( Metamynodon ) Zone 3. 



Mesohippus trigonostylus sp. nov. 

 Plate 2.5,6. Text Fig. 27. 



Horizon and locality. — Cheyenne River, Big Badlands, South Dakota, from the Metamynodon sandstones in the 

 Middle Oreodon beds. Type collected by the American Museum Expedition of 1892 under Dr. J. L. Wortman. 



