DR. E. RAT LANKESTER ON OKAPIA. 303 



The characters of the GirafRdse are as follows : — " Pecora with no canines in the 

 upper jaw, with bifoliate crown to the canines of the lower jaw ; with complete 

 suppression of the second and fifth digits of both fore and hind feet ; without lacrymal 

 fossa; with horn-bosses or ossicusps of variable position (frontal, parietal, occipital, and 

 nasal) not necessarily restricted to a single pair, often one or all rudimentary. In the 

 living genus Giraffa the horns are vellericorns, but probably in some extinct genera 

 they developed a horny theca (cavicorns), and in others may have been exposed as 

 naked antlers." 



Using the foregoing definitions of the groups Pecora and Giraffidae, the genus Okapia 

 may be characterized as follows : — 



" GlEAFJriDiE WITH A PAIK OF SUPKAOEBITAL FKONTAL HOEN-BOSSES, BEARING IN THE 

 ADULT WELL-MARKED CONICAL BONY HORNS OR OSSICUSPS. ThE HOENS COVERED (except 



at the tip) by haiky integument, not by a keeatose theca. A median tumescence of 



THE nasal bones, BUT NO MEDIAN HORN (OSSICUSP). PLANE OP THE BASICRANIAL AXIS AND 

 THE BASIFACIAL AXIS APPROXIMATELY PARALLEL. ArCH FORMED BY THE FRONT TEETH OF 



lower jaw small and narrow; individual incisors and canines relatively very small. 

 Outer ears large." 



N.B. — Okapia is thus contrasted with Giraffa, in which the paired horn-bosses are 

 parietal instead of frontal, and in which also a median frontal tumescence and bony cap 

 develop ; and with Helladotherium, in which there are no paired horn-bosses. It is 

 further contrasted with Giraffa (and all other Girafiidae) in respeot of the small size 

 of its mandibular arch of incisors and canines. This is the only point in which it 

 diff'ers from Samotherium {Palceotragus), unless further study of tiie nature and 

 development of the frontal horns should establish a diff"erence between it and this 

 genus. It difi"ers from Giraffa in the great size of its external ears. 



The genus Okapia contains a single species, 0. johnstoni— the Equus johnstoni of 

 Sclater (P. Z. S. 1901, vol. i. p. 50). The species was originally based upon pieces of 

 the striped skin from the hind limbs, and may be defined as follows : — 



O. JOHNSTONI (Sclater). Okapia with the hind limhs (rump, femoral and tibial region) 

 striped with alternate bands of blackish brown and white ; tarso-metatarsal region 

 white : /ore ZimZis marked with a shackle-pattern — black on a white ground — on the 

 carpus and metatarsus, radial region transversely striped. Body, neck, rump, and 

 upper part of fore limbs a uniform rich reddish brown ; side of the face white, top 

 of the head reddish brown. Tail brown, tapering, with subterminal tuft of long hair. 

 Mane absent. 



vol. XVI. — PART VI. No. 4. — August, 1902. 2 x 



