8 University of California Fuhlications in Zoology [Vol. 21 



reentrant angles on inner and outer sides; most posterior reentrant 

 angle is on outer side, this sometimes deep enough to meet inner 

 reentrant angle subtending the terminal loop, thus isolating a third 

 outer triangle and a fourth inner triangle and reducing the anterior 

 loop to a wedge-shaped loop. Rarely the extreme anterointernal border 

 of loop shows traces of a supplemental reentrant angle. Inner side 

 of tooth with five well developed reentrant angles ; outer side of tooth 

 with three deep reentrant angles and a shallower fourth one. Outer 

 reentrant angles wider than, but of equal depth with, those of inner 

 side. Outer triangles slightly smaller than those on inner side. Poste- 

 rior loop slightly oblique, narrowly crescentic, slightly curved, its 

 inner limb much the longer, its transverse diameter about equal to 

 that of greatest width of crown. 



Second lower molar with transverse posterior loop, two inner and 

 two outer closed triangles, and with two outer and two inner reentrant 

 angles. 



Third lower molar with three transverse loops, each side with two 

 reentrant angles, those of inner side much the deeper, the antero- 

 external angle often obsolete ; posterior loop larger than either of the 

 others, more broadly crescentic in outline than terminal loops of M^ 

 and Mh, though not essentially different in form, the outer limb very 

 short ; first and second loops somewhat irregular and variable in form, 

 the first usually truncate externally, the second usually with an 

 angular projection at outer side. Third lower molar may have the 

 second loop constricted in middle to form two small closed triangles. 



Remarks. — Microtus calif or nims as earlier defined, and even as 

 considered by the most recent workers, proves to be inclusive of a 

 number of races. A large series of specimens from many points within 

 the state has enabled the writer to break up this composite upon 

 seemingly quite adequate grounds. Californicus as now restricted 

 occupies only the central coastal region of California between Pozo, 

 San Luis Obispo County, on the south and Walnut Creek, Contra 

 Costa County, on the north. When still more specimens are available 

 the indications are that it will be necessary to subdivide this form 

 yet farther, recognizing the salt marsh form around the south arm of 

 San Francisco Bay as a different race from that in the adjacent hills. 

 The individuals which live in the marshes are much blacker than those 

 that live on the grassy hillsides. The hill form, so far as the present 

 series shows, is larger and its skull possesses more strongly developed 

 longitudinal ridges. 



Appeal to Dr. T. S. Palmer, of the staff of the United States Bureau 

 of Biological Survey, has made it possible for the present writer to fix 

 the type locality of Microtus californicus californiciis more exactly 

 than has been done previously. Peale's original manuscript journal 

 has been examined by Dr. Palmer upon request, and this shows that in 



