COE : NEMEKTEANS OF WEST AND NOKTHWEST COASTS. / / 



well marked specific differences either in external characters or in 

 internal anatomy. 



On the other hand, while a larger number of species are identical 

 with those on the Atlantic coast, yet the majority of forms are 

 widely distinct both in general appearance and anatomically. The 

 numerous species of Carinella, Emplectonema, Amphiporus, 

 Drepanophorus, Tetrastemma, Taeniosoma, and the strikingly 

 marked species of Lineus and Micrura of the Pacific coast, have 

 few counterparts on the Atlantic coast, although, as stated above, 

 very similar forms occur in Europe. My personal experience at 

 Naples has served to emphasize rather than diminish the impor- 

 tance of this striking similarity of faunas so remote geographically. 



A number of investigators have observed that other classes of 

 invertebrates collected in Puget Sound showed a similarly close 

 relationship with those of Europe and the Mediterranean. 



Two species {Lhieus viridis and Cerehratulus margivatus) occur 

 in the Mediterranean, on the northern coasts of Europe, on the 

 coasts of Greenland and northeastern America, as well as in Alaska 

 and on the Pacific coast. These are evidently circumpolar forms and 

 their distribution is thereby readily accounted for. CejyhalotJirix 

 linearis and Tetrastemma dorsale may also be looked upon as cir- 

 cumpolar species. 



One of the most important factors, however, in the distribution of 

 marine organisms, namely, the temperature of the water, is not 

 greatly different on the southern coast of California, where many of 

 the species referred to were collected, than it is in the Mediterranean. 

 So that a Mediterranean species when once estabhshed on the 

 Pacific coast, or the reverse, would probably have little difficulty 

 from its environmental conditions. 



It may be reasonably expected that future investigations on the 

 coasts of Japan, northern China, the Kurile Islands, Kamchatka, 

 and eastern Siberia will reveal a much more extended distribution 

 of many of the species herein recorded. The few collections which 

 have been made at the Commander Islands, off the coast of Kam- 

 chatka, have thus far contained only the same species as those found 

 on the coast of Alaska. The climatic conditions and ocean currents 

 are such as to distril)ute species found in Bering Sea, and about the 

 Aleutian and especially the Commander Islands, southward on the 

 western side of the Pacific Ocean along the shores of the Kurile 



