208 MONOGRAPHS OF NORTH AMERICAN RODEXTIA. 



that they might be described in identical terms. The oars are the notable 

 feature; and they have been so carefully and minutely described by Baird, 

 from the same specimens now lying before us, that, as in ease of our diagnosis 

 of Chilotus, we may best repeat his words: — 



"The ears arc low, orbicular, the membrane thickened, the margins or 

 concha] portions much inflected or incurved, like a half open apple-blossom, 

 the concha being inflected all around. The antitragus is well developed, but 

 rather low. The surfaces of the ear appear perfectly naked, with, however, 

 a ciliation of long hairs towards the roots of the concha, on the dorsal surface. 

 A close examination of the auricle in the dried specimen shows a few scat- 

 tered very short white hairs. The structure of the ear, though in many 

 respects similar to that of A. pinetorum, is yet essentially different. Thus 

 the upper and lower roots of the margin of the ear meet anteriorly so as to 

 form even a low rim to the meatus anteriorly completely enclosing the aper- 

 ture ; the edge of the conch is inflected ; the region inside the auricle, around 

 the meatus, naked, and the antitragus so much developed as to be capable of 

 completely closing the meatus. In A. pinetorum the roots of the upper and 

 lower margins of the ear are widely separated, by a space of a quarter of an 

 inch, the space between these roots and anterior to the meatus being perfectly 

 plane ; the edges of the concha or auricle not inflected at all ; the inner space 

 around the meatus partly hairy; the antitragus very slightly developed, not 

 valvular nor capable of closing the meatus at all." 



The skull of this species (fill) is rather broad for its length (0.92X0.51), 

 but has nothing diagnostic about it except the dentition, which curiously 

 unites that of Mymwm.es with that of Pedomys or Pitymys. Thus, the 

 middle line of enamel on the front lower molar extends so far forward as 

 to separate the anterior on angles each side, and cut these off" from the dentine 

 island of the anterior trefoil, so that an additional closed triangle is produced 

 on each side. The middle upper molar develops no snag on its postero- 

 external triangle ; and the last upper molar has but one external angle and a 

 long narrow posterior Y. 



A miserable specimen from Oregon (No. 3734, U. S. Expl. Exped.) is 

 labeled "oregona", but is not this species at all, being a Myonomes. The 

 measurements of the three specimens below given will show to some extent 

 the variations in size and shape. At present, the species is only reported from 

 the Pacific coast of tin; United States. 



