190 1.] Gidley, The North A7nerican Species of Equtis. 1 1 9 



the original plate, Phil. Trans., pi. Ixi, fig. i.) An examina- 

 tion of this figure shows that not a single tooth in the one series 

 corresponds at all closely with its opposite in the other series. 

 Not only are the comparative measurements different, but the 

 enamel foldings are so radically different in the corresponding 

 teeth of the two series as to make it very certain that the speci- 

 men is a composite of two individuals. 



A comparison of the two series in any skull of any species of 

 Equiis will show the reasonableness of this conclusion. These 

 differences, however, are entirely within the range of individual 

 variability and of changes due to age. The relatively shorter an- 

 tero-posterior diameters of the teeth (especially of m^- and m^), the 

 relatively less length of the entire series and the relatively greater 

 posterior extension of the maxillary beyond m-^, all indicate that 

 the series of the left side is of an older individual than that of 

 the right. 



Although the principal character assigned to this species by 

 Owen must be disregarded, there remain still enough other 

 characters to define it fairly well. Two of the characters 

 pointed out by Owen, which are shown in both series of his. 

 type specimen, seem worthy of consideration, namely, the 

 comparatively small size of m-S^ and of the anterior lobe of 

 p-^-. Evidently the comparatively small size of m^ is not due 

 to a little-worn condition of these teeth, as the compara- 

 tively small antero-posterior diameters of the other molars, 

 especially in the series of the left side, indicate that it, at 

 least, is of an old individual with all the teeth much worn. 

 Cope seems to suggest, in his article above referred to, that 

 Owen might have taken this character from an imperfectly pro- 

 portioned photograph of the specimen, for he remarks: " This 

 appearance could be produced by the oblique angle of the aper- 

 ture of the camera in photographing, due to its too anterior 

 position." ' This view, however, seems scarcely worthy of con- 

 sideration, as the other teeth seem to be not at all disproportioned, 

 and had so great a distortion of m^ been produced m-^- at least 

 would have been affected to a perceptible degree also. Moreover 

 it is evident, from reading Owen's descriptions of the species E. tau 

 and E. conversidens, that, although, as he states, his descriptions 



' Proc. Acad. Sci. Phila., 1884, Vol. XXII, p. 13. 



