46 



osborn: OLIGOCENE, MIOCENE, pliocene equid.e. 



Acad. Nat. Sci. Phila. Vol. V, (1850), 1851, p. 122.) This skull ("Ancient Fauna of Nebraska," PI. x, figs. 20, 21, PI. xi, 

 figs. 1, 2), superior molar teeth (PI. xi, figs. 3, 4), and inferior teeth (PI. x, figs. 12, 16, PI. xi, figs. 5-8) were again 

 referred to by Leidy as his type and cotypcs (1853), as follows: "The specimens which we have an opportunity to study 

 are as follows: — 1. Cranium proper, with a portion of the face containing on one side the last tooth and the other the last 

 three molars .... The specimen was accompanied by several fragments of a lower jaw of which two contain the last two 

 molars and one has the coronoid process nearly entire." ("Ancient Fauna of Nebraska," 1853, p. 68). Unfortunately 

 these types and paratypes have not all been preserved. Part of the material described in Leidy's memoir of 1853, frag- 

 ments of lower jaws (figs. 5-8, PI. xi) are in the U. S. National Museum collection. (Gidley, letter Nov. 21, 1917) 

 " The complete list of the [U. S. National Museum] pieces, now located in our collection, described or figured by Leidy as 

 representing M. bairdii (Leidy) is as follows: 1. Posterior portions of both lower jaws. 'Ancient Fauna of Nebraska,' 

 1853, PI. xi, fig. 5. (Mentioned on p. 68, of this work, as having accompanied the skull portion (not yet located) first 

 described. I presume the skull and the jaw portions are parts of the same individual.) [? The type.] Cat. No. 8632. 

 2. Upper and lower jaws of both sides. PI. x, fig. 14; PI. xi, figs. 3, 4, 6, 7, and 8, Cat. No. 2359. 3. Portion of left 

 lower jaw. PI. x, fig. 15, Cat. No. 8633. 4. Unworn rt. lower molar, PI. x, figs. 16 and 17, Cat. No. 8634. 5. Skull 

 and lower jaws. ' Fxtinct Mammalian Fauna of Dakota and Nebraska,' 1869, p. 303, Cat. No. 3812." 



Measurements: Type (Leidy, 1851, p. 122). 



"Length of range of seven superior molars, ......... 28-10 inches" 



" " " " " inferior " 3 



"Breadth of face on line with posterior superior molars ....... 1-\ " 



Type measurements estimated from Leidy's figures (Osborn, 1917): m 1-3 .032; m 1 a. p. .011 X tr. .014. 



Fig. 26. Mesohippus bairdii Leidy, Amer. Mus. 1477, neotype (Osborn). After Osborn, 1904. (Left) Superior 

 grinding teeth, fig. 3, p. 172; (right) skull, PI. v, B. Skull one-half natural size, teeth natural size. 



Type figure— Text Fig. 25 of this Memoir. 



Characters. — (Leidy, 1851, p. 122) Type. "This species is about two-thirds the size of P. crassum. The arrange- 

 ment of the superior molars is very like that of Paheotherium Hippoides. . . .This second species Dr. L. named P. bairdii, 

 in honor of Prof. S. F. Baird, Curator of the Smithsonian Institution." 



Neotype. — (Osborn, 1904, p. 172) "A skull and skeleton, No. 1477 Amer. Mus. almost identical with Leidy's type, 

 was found in the Lower Oreodon Beds of South Dakota." 



Type and neotype characters. — (Osborn, 1904, 1918) (1) Skull with a distinct lachrymal fossa; (2) cranial (orbito- 

 postorbital) region exceeds facial (preorbital) region in length; (3) molars with crests interrupted and moderately elevated; 

 (4) small hypostyle present as a small bud or crest connected with posterior cingulum; (5) protoloph tending to 

 unite with parastyle, interrupted by protoconule; (6) metaloph relatively sharp and continuous; (7) parastyle tending to 

 connect with protoloph; (8) internal cingulum present in medivallum of m 3 only. 



