56 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



approximately the same size. South of this, along the north- 

 ern coast of California southward to the Golden Gate, is marin- 

 ensis, paler colored again, practically the same color as the 

 Vancouver Island bird, but smaller. Spilurus, from south of 

 San Francisco Bay, is still paler but a trifle larger, gradually 

 merging, both in color and size, into the larger and more pallid 

 charientiirus of southern California. 



The two birds at hand from the vicinity of Humboldt Bay 

 are typical of marinensis. They are like the average of Marin 

 County birds, and are correspondingly unlike calophonus of 

 the mainland farther north. In the series from Marin and 

 southern Mendocino counties there are several notably pale 

 colored specimens. A female from San Geronimo (no. 2158, 

 Mailliard coll.) is quite grayish above, and there are several 

 juvenals from southern Mendocino County also aberrantly 

 colored. Such a bird is mentioned by Ridgway (1904, p. 565, 

 footnote), from Nicasio; so altogether, it evidently is not un- 

 common to encounter such pale colored individuals at this 

 point. This is at once suggestive of exactly similar condi- 

 tions found prevailing among the bush-tits (Psaltriparus) of 

 the region (see Swarth, 1914, pp. 513-515), and it would 

 seem that in both instances the phenomena are to be explained 

 in the same way. 



The conditions described as probably explanatory in the 

 case of the bush-tit are as follows: "Marked restriction of 

 territory appropriate to the humid coast races, ineffective bar- 

 riers interposed against complementary forms of much greater 

 numbers occupying adjacent territory, and continual encroach- 

 ment of individuals (the radiating overflow) of the latter sub- 

 species" (Swarth, loc. cit.). The genus Thryomancs appears 

 to offer a parallel instance, though to not so marked an ex- 

 tent as in Psaltriparus. Aberrant individuals occur as men- 

 tioned above, in a manner similar to that observed in the latter 

 genus, but not so numerously. 



A series of juvenals from Marin County is appreciably 

 less bright reddish above than is the case in young birds of 

 spilurus from Palo Alto. A series of juvenals from Mendo- 

 cino County contains several pale colored individuals, more 

 nearly approaching the coloration of drynioccus. 



