340 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



5. In manv respects the postorbital processes included in this 

 division resemble the postorbital processes found in that section of 

 the genus Lcpiis which forms the subgenus Pcecilohgns, but on the 

 whole they are rather slenderer, and do not project so far out- 

 ward from the side of the skull. The typical form is seen in 

 Syhilagiis (Microlagus) bachaiani. The postorbital process is at- 

 tached by a comparatively narrow pedicle. A large posterior notch 

 is formed between the sides of the skull and the slender posterior 

 portion of the postorbital process. In No. 63,957, Microlagus from 

 Posts, California, the posterior extremity of the postorbital almost 

 touches the cranium. Sylvilagus {Microlagus) cinerasccns shows 

 conditions of the postorbital ranging all the way from those found in 

 No. 63,957 to conditions almost identical with those found in typical 

 Sylvilagus, but the posterior clavate foramen is always wider in 

 Microlagus. 



6. The postorbital processes of the skulls of the genus Brachy- 

 lagus are small and slender, free both in front and behind. They 

 bear considerable resemblance to the postorbitals of the subgenus 

 Poscilolagus. 



7. The genus Liiiinolagus possesses postorbital processes of a 

 form quite different from any of the others. The process is com- 

 pletely fused to the side of the frontal bone so that only a notch is 

 found anteriorly and no notch or slit is found posteriorly except in 

 rare and anomalous cases where a small foramen is sometimes seen. 

 The fused postorbital process has about the same general shape as 

 has the unfused process of the genus Sylvilagus. An atypical 

 specimen. No. 64,029, Kissimmee, Florida, shows the manner in which 

 the process is attached. The posterior end of the process, instead 

 of meeting the skull directly as it does in those genera where the 

 posterior end of the process is in contact with the side of the skull, 

 is met by an outgrowing process from the cranium. In this speci- 

 men, No. 64,029, a small foramen is inclosed between the posterior 

 part of the postorbital process and the above outgrowing process 

 from the cranium. A more or less prominent blunt projection is 

 formed by the union of the postorbital process with the outgrowing 

 process from the cranium. This blunt projection above, together 

 with the root of the zygomatic process just below, forms a rather 

 conspicuous notch. 



INTERPARIETAL BONE 



The interparietal bone of the Leporidse is always present in the 

 very yovmg, and in most cases remains perfectly distinct in the adult. 



