22 Proceedings of the Biological Society of Washington. 



those of chryseola by outline of nasals. In humboldtiana the embayment 

 in the lateral outline tends to be more pronounced and situated farther 

 forward than in chryseola. Interpterygoid fossa usually broader; paroc- 

 cipitals lighter; measurement transversely across angular process of 

 mandible less. 



Comparisons. — Examples of Aplodontia humboldtiana are larger and 

 less richly colored than topotypes of A. pacifica from Newport, Oregon. 

 From the new form one receives the impression of black interspersed with 

 bufly, while from pacifica one gets the impression of rich brown, with 

 black hairs plentifully insprinkled, and especially emphasized on the 

 middle line of the back. A. humboldtiana is not so black as A. nigra, 

 which is the darkest member of the genus known to date. The new form 

 is less rich in brown coloration than any of the species occurring in con- 

 tiguous districts, with the possible exception of nigra, chryseola being 

 next in degree of richness, and pacifica the brightest of all. A. hum- 

 boldtiana is also marked off from all its neighbors by the faint brown 

 wash ventrally. In nigra the ventral brown wash is more distinct, in 

 chryseola still more distinct, and in pacifica the most distinct of all. 



Cranially Aplodontia humboldtiana can usually be separated from A. 

 pacifica by the broader outline of its nasals, which are in most examples 

 conspicuously dilated anteriorly rather than straight as in the Oregon 

 species. Zygomatic width tends to be greater in humboldtiana than in 

 pacifica or A. nigra, more as in A. chryseola. In general the cranial 

 measurements of the new form tend to be greater than in pacifica or 

 nigra. Nine of the fifteen specimens of humboldtiana measured have 

 the width of the interpterygoid fossa equal to or exceeding the maximum 

 of this measurement in chryseola and pacifica. A. humboldtiana has 

 paroccipital processes intermediate in condition between the less promi- 

 nent, more plate-like type observed in most examples of pacifica and 

 the more prominent, heavier, more knob-like type noted in chryseola. 

 Measurement transversely across angular process of mandible practically 

 the same in humboldtiana as in pacifica, less than in chryseola. But 

 greatest length of mandible links humboldtiana with chryseola rather 

 than with pacifica. This measurement aff"ords a separative character as 

 between humboldtiana and nigra, also, being greater in the former than 

 in the latter. 



Material. — Twenty-one specimens, all from California: 8 (Nos. 21,155- 

 21,162, Mus. Vert. Zoo!., taken by H. E. Wilder) from Carlotta, Hum- 

 boldt County; 7 (No. 11,413, Mus. Vert. ZooL, taken by Frank Stephens; 

 Nos. 18,990-18,994, 19,174, Mus. Vert. ZooL, taken by H. E. Wilder) 

 from Cuddeback, Humboldt County; 5 (Nos. 9061-9064, 9066, Field Mus. 

 Nat. Hist., taken by E. Heller) from Eureka, Humboldt County ; 1 (No. 

 21,983, Mus. Vert. ZooL, taken by H. S. Prescott) from Requa, Del Norte 

 County. 



Measurements. — Type (adult male) : Total length, 365 mm. ; tail verte- 

 brae, 35; hind foot, 58; basilar length of skull, 59.8; width of nasals, 

 10.5; length of audital tube, 19.4; length of incisive foramina, 7.5; zygo- 

 matic width, 53.9; greatest width of interpterygoid fossa, 5.5; mastoid 



