192 University of California Publications in Zoology [Vol. 10 



6. Eallus obsoletus (California Clapper Rail). 



Inhabits the salt marshes of the south arm of San Francisco Bay. 

 Characterized by large size and pale tone of coloration. Nearest relative, 

 L'nlliis levipes of the salt marshes of the coast of Southern California. 



(Should close study be accorded the Marsh Wrens (Telmatodytes) 

 of the San Francisco Bay marshes, it is not improbable that differences 

 ■would be found. This Museum still lacks material for such inquiry.) 



Mammals 



1. Reifhrodontomys raviventris (Red-bellied Harvest Mouse). 

 Inhabits the salicornia flats mi the salt marshes surrounding the south 



arm of San Francisco Bay, at least from Redwood City around to Mel- 

 rose. Characterized by small size and dark colors, reddish beneath. 

 Nearest relative, R. longicauda of the fresh water riparian and meadow 

 associations of the immediately adjacent uplands. 



2. 'Reifhrodontomys halicoetes (Tidal Marsh Harvest Mouse). 

 Inhabits the salt marshes on the north side of San Francisco Bay, at 



least at Petaluma, and the brackish marshes of Suisun Bay from Cor- 

 delia Slough to Grizzly Island. Characterized by great size and dark 

 coloration. Nearest relative. R. longicauda of the fresh water riparian 

 and meadow associations of the adjacent uplands on all sides. 



3. Microtus edax (Tule Meadow Mouse). 



Inhabits the marshes of the Suisun district, from Cordelia Slough 

 eastward to the confluence of the Sacramento and San Joaquin rivers, 

 and up each of these streams for an unknown distance. Characterized 

 by great size and dark coloration. Nearest relative, M. califomicus of 

 the adjacent uplands on all sides. 



(The meadow mouse of the marshes on the north side of San Fran- 

 cisco Bay resembles edax in slight degree, but has not so far been 

 recognized as separable from califomicus. The meadow mouse of the 

 marshes of the south arm of San Francisco Bay is at present considered 

 the same as califomicus of the surrounding uplands.) 



4. Son i halicoi lis (Salt Marsh Shrew). 



5. Sorest sinuosus (Suisun Shrew). 



These two species are dealt with in detail on preceding pages. 



INFERENCES 

 Tlir foregoing data point towards the existence of three 

 differentiation areas in the salt or brackish marshes of the San 

 Francisco Bay region, each cut off by barriers (to pahistrine 



animals) from both of the other two. These areas are: (1) the 

 marshes bordering the south arm of San Francisco Bay; (2) the 

 marshes along the north side of San Francisco Bay (including 



