RODENTIA. 177 



the cerebellum and olfactory lobes entirely exposed. The latter are ovoid 

 and expanded laterally. 



The coranoid process of the mandible is large and high, as in Arctomys. 

 The condyle is small and compressed. The angle is produced, so that the 

 posterior border of the ramus is concave. 



Associated with the skull of a P. delicatissimus are various parts of the 

 skeleton. A lumbar vertebra is not elongate ; its anterior articular face is 

 slightly convex and the posterior plane. The outline of the former is a 

 little more than half a circle. The diapophyses are large, and are opposite 

 the floor of the neural canal. The prezygapophyses are subvertical, and 

 the superior exterior edges are developed into well marked metapophyses. 

 The middle line below has a low narrow keel, which separates two large 

 nutritious foramina. 



The proximal part of the scapula is preserved. It resembles in gen- 

 eral that of a squirrel, having a recurved coracoid process, and a well 

 developed acromion. The latter is quite flat, and is continuous with a hori- 

 zontal expansion of the spine. The humerus has a subround head, and the 

 tuberosities are little prominent, and enclose but a shallow bicipital gi-oove. 

 The deltoid crest is prominent, and extends to the middle of the shaft. Its 

 inferior portion is more prominent and compressed than the superior por- 

 tion. The teres facet is well marked. The distal end is transversely 

 extended by the large size of the internal epicondyle. The condyles are 

 simple hour-glass-shaped, and without crest. The epitrochlear foramen is 

 distinct. The ulna and radius are long and slender, and their carpal arti- 

 cular surfaces are of subequal size. The head of the radius is nearly 

 round. Two metacarpals are preserved, and they are rather short ; there is 

 an inferior trochlear keel of the distal articular extremity. 



The pelvis is much like that of a squirrel. The ilium is not much 

 expanded towards the crest, but cannot be called prismatic. Its external 

 rib is near the anterior border, and the posterior edge is thin, and bounds a 

 concavity of the external face. The anterior inferior spine is prominent 

 The ischium is two-thirds the length of the ilium, and is moderately 

 expanded distally in a vertical plane. Its spine is distinct Fragments of 

 femora, associated with the other specimens, have the characters of those 



