48 AMERICAN HYDKOIUS. 



MEDITERRANEAN. Including the Mediterranean proper and the Adriatic. 



The other regions named are self-explanatory. The few cases where American species are 

 found in regions not mentioned above are indicated in footnotes. 



It will ! seen that most of these regions are quite arbitrary, and their fauna' intergradc in 

 almost all cases. Until a more serious and comprehensive study is made of the distribution of 

 all groups of marine organisms no final or even approximately satisfactory set of zoogeographical 

 regions can be made. In the meantime, however, each worker can exercise his own judgment 

 in devising a scheme that will satisfy his special requirements and aid him in indicating the facts 

 of distribution so far as his field of work is concerned. It remains for some master mind to 

 correlate these various attempts into a well-digested zoothalassography. 



The table given above will serve to indicate some points of interest, the most notable being 

 the richness of the sertularian fauna in the Alaskan region, in which 5X of the 181 species of 

 American forms are found. This ma}' be due to the excellent work done in that region, 

 beginning with the extensive collections made by Dr. Dall and his party, 1 and terminating with 

 the notable collections made by the Harriman Alaska Expedition. 2 In the meanwhile the U. S. 

 Fish Commission steamer A/?><tfrxx made very extensive collections during her several cruises in 

 Alaskan waters, the material of which is included in the present work. 



Next to this region come the West Indian and the Arctic, with 35 and 29 species. An 

 examination of the table clearly reveals another fact, and that is that the sertularian fauna seems 

 to have its present center of distribution in the far north, probably in the Arctic regions, as is 

 indicated by the holarctic distribution of many species a matter that the present writer has 

 already discussed. 3 



In working with material from the far north, particularly from Alaska, one is greatly 

 impressed with the luxuriance and thrifty appearance of the hydroids an indication that the 

 region is peculiarly adapted to their needs. The, finest specimens, both of campanularian and of 

 sertularian colonies, that the writer has ever seen came from the cold waters of Alaska. The 

 various Scandinavian writers have found a rich field for work in the hydroids, and Kristine 

 Bonnevie has produced a sumptuous monograph on the Hydroids of the Norwegian North Atlantic 

 Expedition. It seems, then, that the group has spread from the Arctic region southward on 

 both shores of the Atlantic and on the Pacific coast of North America, and there are so many 

 species common to these four regions that we can hardly escape the conclusion that the group, 

 at least in its present forms, had a polar origin. The number of species found in the West 

 Indian region would seem to militate against this view, but many of these belong to special 

 groups, such as the Desmosoyphus group of Sertularia, indicating that they have long been 

 separated from the ordinary types of the family. The Sertularidse appear to have .spread, from 

 whatever center, over the ocean floor throughout the world; at least they have been found in 

 every region where any considerable amount of dredging has been done. They must be quite 

 abundant in the, Patagonian region, for the small amount of collecting done there has given us 

 no less than seventeen species. Australia also has a rich sertularian fauna of about sixty species, 

 according to Bale, 4 which seems to be rather closely allied to the Patagonian forms, indicating 

 the possibility of an Antarctic center of distribution, for certain groups at least. The west 

 coast of South America seems to be the poorest in Sertularidse of all the American regions 

 included in the table. This may be due to the comparatively few hauls made in these waters, 

 but probably indicates a real dearth in that region. 



It is interesting to note the great difference shown in this table and the one on pages 4! to 

 51 of Part I of this work between the distribution of the Sertularida? and the, Plumularidse, the 

 former having its greatest wealth of material in the Alaskan region and the latter in the West 

 Indies. 



1 See Clark, Report on the Hydroids collected on the Coast of Alaska and the Aleutian Islands by W. H. Dall, 

 Proceeding, Academy of Natural Sciences of Philadelphia, 1S7H. 



2 See Papers from the Harrinum Alaska Kxpedition, XXI, The Hydroids, ('. C. Nutting, Proceedings Washington 

 Academy of Sciences, III, 1901, p. 157. 



3 Hydroids of the Harriman Expedition, 1901, p. 161'. 



4 Catalogue of the Australian Hydroid Zoophytes, W. M. Bale, Sydney, 1884. 



