42 



NOETH AMEBICAK FAUKA. 



[No. 36. 



It is apparently confined to the salt marshes in the southern part of 

 San Francisco Bay and although in many places its range abuts on 

 that of longicaudus, no evidence of intergradation between them has 

 been discovered. Two specimens — one from Palo Alto and one from 

 Berkeley — ^have whitish underparts but in other respects are typi- 

 cal raviventris, Intergradation with lialicmtes seems probable. The 

 pelage of both of these marsh forms is longer and seemingly thicker 

 than that of longicaudus. 



Specimens examined. — Total number, 44, from the following locali- 

 ties: 



California: Berkeley, 2; Elmhurst, 1;^ Melrose Marsh, Alameda County, 13;^ 

 Palo Alto, 4;2 Redwood City, 24. ^ 



REITHRODONTOMYS RAVIVENTRIS HALICCETES Dixon. 

 Petaluma Marsh Harvest Mouse. 

 (PL I, fig. 10; PL IV, fig. 10.) 

 Reithrodontomys haliccetes Dixon, Univ. Cal. Pub. in ZooL, V, 1909, p. 271. 



Type locality. — Salt marsh 3 miles south of Petaluma, Cal. 



Distrihution. — Salt marshes of San Pablo Bay, Suisun Bay, and the 

 lower San Joaquin and Sacramento Kivers. 



Characters. — Similar in color to raviventris but larger; underparts 

 white; ears and feet paler; tail more distinctly bicolor. Compared 

 with B. m. longicaudus: Decidedly larger and darker, with a large 

 white patch on the throat; skull larger, with more widely spreading 

 Z37'gomata. 



Color. — Fresli pelage: Upper parts ochraceous-buff, heavily mixed 

 on the back with black; sides ochraceous-buff without a well-defined 

 lateral line; underparts white (the bases of hairs plumbeous), some- 

 times irregularly blotched with ochraceous-buff; throat and sides of 

 mouth pure white to base of hairs; sides of nose and eye ring blacldsh; 

 ears and upper surface of tail fuscous or fuscous-black; underside of 

 tail dull grayish white with a buffy tinge; feet white or buffy white. 

 Worn pelage: Decidedly more ochraceous, the black tips of the hairs 

 seemingly worn off. 



Slcull. — Similar to that of raviventris; larger than that of R. m. 

 longicaudus; zygomata usually (at least in adults) widely expanded 

 anteriorly. 



Measurements. — Average of 13 from type locality: Total length, 156 

 (149-64); tail vertebrse, 82 (75-85); hind foot 17.7 (17-19). Skull: 

 (See table, p. 81). 



BemarTcs. — This form, although living only a short distance from 

 raviventris and under seemingly identical conditions, is readily sep- 

 arable from it. Nor is it in any sense a connecting form between 



1 Collection Mus. Vert. Zool., Univ. of Cal. 2 Three from Collection Mus. Vert.Zool. 



