224 [January, 



describing a new species of pouched Eat, of the genus Dipodomys, Gray; 

 which was referred to Dr. Bridges, Dr. Le Conte and Mr. Cassin. 



Dr. Le Conte offered some remarks on the genus Dipodomys, and stated that 

 he had recently been investigating the specimens of that interesting genus in 

 the Collection of the Academy, and had come to the conclusion that it contained 

 several species besides those already known. The fortunate arrival of an un- 

 doubted specimen of D. Phillipii (Gray) from California, and which, by the 

 liberality of Dr. Heermann, is now in the possession of the Academy, has 

 enabled him to complete the study of this genus, and the results will soon be 

 made known to the Academy in a monograph, now in preparation by himself, 

 on the North American Myoxina. 



He exhibited to the members five species of Dipodomys, and pointed out their 

 specific characters, which are to be found in the length and color of the tail, and 

 in the form of the antitragus of the ears. In other respects, both in form and 

 color, the species resemble each other very closely. These differences, he 

 stated, could not be the result of age, as the specimens, with one exception, 

 were full grown; he stated, moreover, that the specific differences were similar 

 to those found in the genus Myoxus, tpw'hich, by the form of the scull, and by 

 the absence of the postorbital process, the genera Dipodomys and Perognathus 

 show the closest resemblance. With the group of Dipoda, in which the former 

 genus is placed by European systematists, these genera have no relation. The 

 five species known to him may be thus grouped. 



A. Tail much longer than the head and body, furnished towards the tip with 

 a brush of long hairs ; antitragus short, broad and very distinct. 



1. D. Phillipii Gray, Ann. and Mag. Nat. Hist. 7,522: Audubon, 

 Quadr. of America, pi. 130: Wagner, Schreber's Saiigeth: Suppl. 3, 295. Schintz, 

 Syn. Mam. 2, 93. 



Tail brown, with a whitish vitta each side; outer third dark blackish brown ; 

 tip pure white. Sacramento Valley; Dr. Heermann. 



2. D. agilis Gambel, Proceedings Acad. Nat. Sc, 4, 77. 



Tail brownish, with an indistinct whitish vitta each side ; outer third to tip 

 nearly uniform pale brown. San Diego ; Dr. John L. Le Conte. 



B. Tail as long as the head and body ; hair at the tip scarcely longer ; anti- 

 tragus very short, indistinct. 



3. D. Heermanni. Tail brown, becoming black towards the extremity, 

 with a broad white vitta each side ; tip pure black. Sierra Nevada; Dr. Heer- 

 mann. (Specimen not quite adult.) 



C. Tail shorter than the body ; hairs on the outer third very long ; ears mode- 

 rately small ; antitragus obsolete. 



4. D. Ordii Woodhouse. Tail brownish, with a broad white vitta each 

 side ; long terminal hairs pale brown, white at the base. El Paso, Texas ; Dr. 

 Woodhouse. 



Of the fifth species there is a single specimen labelled " James Read, South 

 Carolina ;" this locality seems doubtful, as all the other species are from the 

 western part of the continent. It seems to belong to the first division, although, 

 as the outer portion of the tail is wanting, we cannot be certain of that fact. 

 The length, however, of the individual caudal vertebrae, indicates a tail similar 

 to that of D. agilis, with which it agrees in color. The ears are somewhat 

 larger than in that species, and the antitragus is large, broad and obtusely 

 rounded at its summit. For this species the name D. Wa gner i is proposed. 



Of Perognathus there are now three species known. 



1. P. fasciatus Wied, Nova Act. Leopold Car. Acad. 19, 369, tab. 34 ; 

 Wagner, Schreber's Saugeth. Suppl., 3,G12; Schintz, Syn. Mam., 2, 259. Mis- 

 souri Territory. 



