lvon] the kares and their allies 397 



posterior limb touching the side of the cranium and helping to bound 

 a clavate foramen. Rarely the process fails to meet the cranium. 



Skull (pis. Lx\i, 7-10; Lxvii, I, 2; Lxxxvi ; lxxxvh). — The post- 

 orbital processes are long and narrow, attached to the skull 

 by a very broad pedicle. The whole anterior part of the process, 

 with the exception of a millimeter or two, is attached to the 

 skull and a very small anterior notch is thus formed. The 

 posterior part of the postorbital process is long and narrow, 

 not triangular. Its inner posterior edge usuallv touches the 

 cranium and the process thus forms a narrow clavate slit. The 

 amount of fusion of the postorbital process is subject to consider- 

 able variation. In one individual, Sylrilagus Horidanns mearnsi, from 

 Illinois, complete fusion of the postorbital with the side of the skull 

 takes place and the usual clavate slit is obliterated. In Syk'ilagus 

 arizoncc and its forms the anterior portion of the postorbital process 

 is not so extensively fused with the frontal bone and a larger 

 anterior notch is found than in the more typical forms. In the most 

 highly dififerentiated forms of the subgenus Microlagus, viz., bach- 

 mani, the postorbital process is attached by a comparatively narrow 

 pedicle, a large notch is found in front, and as the posterior end of 

 the postorbital does not meet with the cranium a large notch is found 

 posteriorly instead of the usual clavate slit. In No. 63,957, Sylvilagtis 

 bacJunani, from Posts, California, the posterior extremity of the 

 postorbital almost touches the cranium. Skulls of 5^. (Microlagus) 

 cinerasccns show conditions ranging from those seen in No. 63,957 

 to conditions very similar to those found in typical Sylrilagus, but 

 the posterior clavate slit is always relatively wider. Intermediate 

 conditions are thus found from the extreme freedom of the post- 

 orbital seen in 5". bachmani, No. 35,131, Nicasio, California, passing 

 through 6^. cinerasccns and then 5. ariconcc and normal typical Sylzn- 

 lagus, to the atypical skull, from Illinois, No. 22,409, where the 

 postorbitals are entirely fused to the sides of the cranium. 



The bony palate in true Syli'ilagus is rather short, slightly larger 

 relatively than it is in Lcpus or Brachylagus, but shorter than in 

 any of the other genera. Its length half-way between the median 

 line and the dental alveoli about equals the greatest width of the 

 incisive foramina and also the distance between the vertical plates of 

 the palate bones. In the Syk'ilagus arizoncc group the palate is 

 shorter than in typical Syli'ilagus: its length half-way between the 

 median line and the dental alveoli is less than the width of the 

 incisive foramina and about equals the distance between the vertical 

 plates of the palate bones, which are here closer together than in 



