256 VERTEBRATE REMAINS, PORT KENNEDY BONE DEPOSIT. 



of the protocone enters the same dimension of the entire crown from two a and 

 third to nearly three times. These measurements are taken so as to include the 

 enamel borders only. In the other plistocene horses of North America, the antero- 

 posterior diameter of the protocone is from one-half to three-fifths that of the entire 

 crown, excepting in the premolars of Equus occidentalis Leidy, and in the larger 

 E. crenidens Cope. I have used this character as diagnostic of species of this 

 genus in my synopsis of the American species published in 1884, and it has unques- 

 tionable value, 1 as the development of the protocone is the one feature which 

 distinguishes the molars of Eqims from those of Hippidium. In the earlier species 

 of Equus the diameter is always small, as in E. cumminsii? In Equus caballus 

 the character is very variable, but the diameter of the protocone generally increases 

 from the front posteriorly. This is not the case in Equus fraternus, where the 

 diameter is the same throughout the series. This species is also characterized by 

 the imperfection of the posterior border of the cusps of the incisor teeth of the 

 lower jaw. This character appears in the inferior series in the collection above 

 referred to. The external incisor has no internal edge, and that of the second is 

 fissured to the base of the cup. It is entire in the i T . In the typical E. fraternus 

 from Florida, the internal cup-border is wanting from the entire series. The superior 

 incisors of the latter are unknown, but in the Port Kennedy specimens the interior 

 border is present throughout, and the anterior face has a shallow, open, longitudinal 

 groove. 



One of the individuals differs from the others in the greater complexity of the 

 enamel plates, especially on the opposed faces of the external lakes, agreeing in this 

 respect with Equus complicatus of Leidy. In the other individual the enamel is 

 less plicate, and is more as in E. intermedius Cope. In the upper molars of all the 

 specimens there is a tendency to crenulation. The specimens from South Carolina 

 which served as Leidy' s types of Equus complicatus, and a superior molar so labelled 

 by Leidy from Luzerne Co., Pennsylvania, are characterized by the considerable 

 anteroposterior diameter of the protocone. All the specimens from Port Kennedy 

 are on the other hand characterized by the very small anteroposterior diameter of 

 this part of the tooth. The examination of a large amount of material leads me 

 believe that this character has greater significance in the extinct species than the 

 degree of complexity of the enamel plication, within certain limits. A specimen in 

 the museum of the Academy of Natural Sciences of Philadelphia has a protocone 

 of exactly the same form and proportions as the Port Kennedy specimens. This is 

 the only individual that has come under my observation which agrees with the 

 series of smaller size now described from Port Kennedy. 



The superior molars displaying moderate complexity, are of smaller size than 

 the complex ones, conforming in this respect to the types of E. fraternus. The 

 molars with complex enamel are of larger size, agreeing in this respect with the 

 typical E. complicatus, and having also the dimensions of E. intermedius Cope. In 



1 Proc. Am. Phil. Soc, 1895, p. 463, PI. XI, fig S. 



2 Report Geol. Survey, Texas, 1893, p. 67, PI. XXII, fig. 7. 



