33^ smithsonian miscellaneous collections [vol. 45 



Leporid.e 

 (Plates LXXIV-LXXXIX) 

 The skulls of the Leporidse fall into several groups, each distinct 

 from the other, and no specimens have been seen which show inter- 

 mediate conditions between any two of the divisions. The varia- 

 tions upon which these groups are founded consist principally in the 

 shape, size, and method of the attachment of the postorbital proc- 

 esses, the distinctness of the interparietal bone, the distance between 

 the two vertical portions of the palate bones, or width of the choanse, 

 and the relative heaviness of the zygoma. Each of these points 

 will be considered in detail. 



POSTORBITAL PROCESSES 



The postorbital processes are conspicuously developed in all of the 

 Leporidne. In general and typically the process is triradiate, one 

 arm being attached to the skull and forming the pedicle of the 

 process, the other two arms or angles being toward the outside, one 

 directed anteriorly, the other posteriorly. The following seven 

 forms of postorbital processes are found : 



I. Postorbital processes large and triangular, standing out from 

 the side of the head and considerably arched from before backward. 

 This form is best developed in the subgenus Lcpus, where the 

 process is a conspicuous triangle, one angle of which is attached 

 to the skull, the other two angles of which are entirely free, the 

 anterior subtending a large anterior notch, and the posterior sub- 

 tending a larger posterior notch. Occasionally in some specimens 

 the anterior angle of the postorbital process is directed inward, its 

 apex meets the frontal bone and a distinct foramen is formed instead 

 of a notch. In the subgenus Macrotolagus the posterior angle of 

 the postorbital process is always directed inward to meet the side of 

 the cranium and in this way forms the outer boundary of a con- 

 spicuous foramen. Some of the Old World specimens resemble 

 Macrotolagus in this respect; such are Lcpits sp. Jumna river, 

 India; L. ochropus, East Africa; L. hypsibius, Ladak, and L. 

 tihetanus, central Asia. In the hares belonging to the subgenus 

 Pacilolagus the postorbital processes, while of the same general 

 form, are much slenderer, the outer angles are not so wide, and the 

 process is not so arched as it is in its best developed form in the 

 subgenus Lepiis. Both anterior and posterior angles are free, and 

 help to form corresponding notches with the rest of the skull. The 

 posterior angle and notch are larger than the anterior angle and 



