[l6l] THE HYDROIDS 179 



also occur to the eastward of the Islands, while five have not 

 been reported from any locality other than the ones where they 

 were originally discovered. Our present knowledge therefore 

 does not support the validity of Dr. Ball's division of faunas at 

 the Shumagin Islands. It rather indicates a continuity of fauna 

 from southern Alaska to the end of the Aleutian chain. Hydroid 

 life appears to decrease as we go westward, but this may be only 

 apparent and due to the more extensive exploration of the shores 

 east of the Aleutian Islands. 



Dr. Dall extends his Oregonian fauna down to Monterey, 

 California. Reasoning again merely from the known distribu- 

 tion of hydroids, it would seem that Puget Sound is a natural 

 region of demarcation between faunae, although the region from 

 Puget Sound to San Francisco has been very little explored. 

 In 1876 Dr. Clark published a paper on ' The Hydroids of the 

 Pacific Coast of the United States south of Vancouver Island,' l 

 in which he gives a list of twenty-four species ; of these only 

 two, Lafoea dumosa and Sertularia argentea, have as yet been 

 reported north of Puget Sound. The same author, in reporting 

 on Dr. Dall's collections from Alaska, notes as one of the main 

 points of interest, the "small number of species that are com- 

 mon to the Alaskan coast and the western shores of the United 

 States from Vancouver Island southward. 2 In 1899 the present 

 writer published a paper on ' Hydroida from Alaska and Puget 

 Sound ' 3 in which it appears that out of twenty-two species from 

 Puget Sound, only four have been reported farther south, while 

 fifteen are now known to occur in Alaska. In the same year 

 Mr. G. N. Calkins published a paper entitled ' Some Hydroids 

 from Puget Sound,' 2 in which some thirty species are noted, 

 only two of which are known to occur south of Puget Sound. 



From this study of the distribution of the Hydroids of the 

 northwest coast of America, therefore, I am strongly persuaded 

 that the region south of Puget Sound constitutes one distinct 

 faunal area, and that the region from Puget Sound north and 

 west to the end of the Aleutian chain constitutes another un- 



1 Trans. Conn. Acad. Sci., Vol. in, pp. 250-251, 1876. 

 2 Proc. Acad. Nat. Sciences, Philadelphia, p. 212, 1876. 

 3 Proc. U. S. Nat. Museum, Vol. xxi, No. 1171, 1899. 

 4 Proc. Bost. Soc. Nat. Hist., Vol. xxvm, No. 13, 1899. 



