ADDITIONAL SIWALIK PERISSODACTYLA AND PROBOSCIDIA. 13 
therefore, be of more than individual value, if all the three first specimens are 
correctly referred to the same species. 
It appears from the foregoing comparisons and measurements that the Perim 
skull ao’rees so nearly witli H. antilopinum that there seems no reason for assigning 
it to another species' ; although its large size tends to remove one of the distinctions 
betvreen that species and H. theohaldi. 
Accepting the provisional reference of the skull under consideration to II. 
antilojjinum, its distinctive characters will be exhibited in the best way, by at 
once comparing it with the skull of II. gracile. Regarding the teeth, no more 
need be said except that there are no signs of the presence of pm. 1 ; which exists 
as a small tooth in some specimens of H. gracile : this absence is the more remarkable 
since this tooth persists in both the Siwalik species of Equus. The Perim skull 
agrees with that of its European congeneP in its comparatively small size ; as well 
as in its general contour, and absolute size. The two skulls also agree in the 
presence of two cavities in the outer surface of the maxilla, one of which (a) may 
conveniently be termed the anterior, and the other (b) the posterior maxillary cavity. 
There is, however, a very great difference in the shape and position of the former 
cavity in the two skulls. In IT. gracile the posterior, or so-called larmial, cavity 
is very large, extending backwards as far as the anterior border of the lachrymal, or 
within less than an inch from the anterior border of the orbit, and having a long 
diameter of more than three inches. The infra-orbital foramen (^trqus sous-orhitaire) 
is described by Prof. Gaudry^ as “ sitiie, soil a la par tie anterieure du larmier^ soil en 
dehors et un peu en avant.^’’ In the Perim skull, on tlie other hand, the corresponding 
cavity (Z>) is comparatively small, and separated by a considerable interval from the 
anterior border of the lachrymal (/«), and by a space of two-and-a-half inches from 
the orbit, its longer diameter being about one-and-a-half inches. The infra- 
orbital foramen commences at the hinder extremity of the posterior cavity ; 
the latter having merely the appearance of a much dilated aperture of the 
foramen. The same cavity extends some distance on to the outer surface of the 
nasal. In advance of the posterior cavity there is a broad, shallow, groove on the 
surface of the maxilla, conducting to the anterior maxillary cavity («;), which is a 
deep spherical dei^ression immediately in advance of pm. 2 . The corresponding 
cavity* in TI. gracile is considerably longer and shallower ; but was apjmrently 
connected with the j^osterior cavity by a similar groove, which the crushed condition 
of the Pikermi skull has to a great extent obliterated. According to Prof. Gaudry^ 
distmct traces of this anterior cavity may be seen in the skulls of E. hurchelli and 
1 Seeing that if the hrohen maxillse of the existing speeies of African horses were mingled together it would prohahly 
he quite impossible to refer them to more than one species, it is highly probable that the teeth and maxillse referred to H. 
antilopinwn really belong to more than one closely allied species. In the absence, however, of any certain points of specific 
distinction, the only course at present is to refer them provisionally to the same species, or group, if the latter term he preferred. 
2 Gaudry, “Ann. Foss, et Geol. de I’Attique,” pi. XXXV.: by the courtesy of Prof. Gaudry the writer has been 
enabled to compare the Perim skull with a cast of the Pikermi specimen. 
3 Op. ct7., p. 222. 4 Marked d in Prof. Gaudr 5 r’s figure. 3 Op. ctV., p. 222. 
D 
