COPE.] PALEONTOLOGY LOUP FOEK EPOCH. 525 



reduced proportions. This is important as distinguishing the genus 

 trenchantly from Eqims ; and while the union of the inner columns of 

 the superior molars distinguishes it from Eippotlierium, a form of P. 

 j^erditus is described below, in which the columns are more distinct than 

 in individuals heretofore known. 



The P. sejunctus is identical in measurements with the P. labrosus, 

 and agrees with it in the simplicity of the enamel boundaries. It is also 

 a short-crowned type, but the character is not so marked as in the latter. 

 It differs strikingly in the deep and convex symphysis, and, in the only 

 specimen in which its alveolar border is preserved, in the hiatus sepa- 

 rating the inferior canine from the incisors. It exhibits also the small 

 . and one-rooted first premolar of the P. percUtus. 



The adjacent horns of the lakes of the molars are more produced out- 

 wardly than the remote ones, and the enamel borders have no plications. 

 The sections of the inner columns are oval posteriorly and subround 

 anteriorly. The wearing of the last molars indicates the full maturity 

 of the animal ; the canines are separated by a considerable interval 

 from the third incisors. The inferior molars are similar in general to 

 those of P. lalrostis ; in three individuals, the last lobe of the last molar 

 is a cylindroid instead of a trough-shaped column. 



The cranium in general form partakes of the shorter and more ele- 

 vated outline seen in all the three-toed horses. The free part of the 

 nasal bones and the diastema behind the canines are short. The outline 

 of the vertex, from the nose to the sagittal crest, is quite plain, while 

 the posterior part of the nasal bones, &c., is much narrowed by the 

 large facial depression at the sides. This occupies the space between 

 the nasal bones and the malar ridge above and below, and is bounded 

 behind by the anterior border of the orbit; in front it is open, but its 

 depression follows below the nasal bones to the diastema. While its 

 area is strongly impressed, especially superiorly and inferiorly, it is not 

 nearly so much so as indicated by Leidy in P. insignis and P. mirabilis, 

 but more marked than in his figure of P. perditus. My specimens of 

 the latter are not well preserved in the region in question. 



The infraorbital foramen issues above the anterior border of the first 

 true molar and the malar ridge above its posterior portion. The orbit 

 is closed behind, and the sagittal crest is but an angle, and originates 

 above the glenoid cavity. The inion is narrowed above, and projects 

 backward over the upper edge of the foramen magnum ; i^osteriorly, 

 the occipital presents a pair of vertical fossse, separated by a low ridge. 

 Its external crest is not continued to that of the squamosal part of the 

 zygoma. The meatus auditorius is quite small, as is also the mastoid 

 tuberosity. The paramastoid is large and stout. 



Measurements of cranium. 



M. 



From occipital condyle to incisor-teeth 0.330 



From occipital condyle to last upper molar 140 



From occipital coudyle to fundus of palatal notch 1G5 



Length of entire molar series 124 



Length of crown of first premolar Oil 



Length of crown of second premolar 025 



Width of crown of second premolar 018 



Length of crown of first true molar .017 



Width of crown of first true molar 020 



Height of crown of first true moKar 013 



Length of diastema 027 



Height of crown of canine 015 



Width of arc of incisors 050 



L(;ngtii from first incisor to first premolar 0(59 



Length from lirst incisor to nasal notch, (oblique) OrfO 



