48 AMERICAN HYDROIDS. 



explored, Great Britam and Australia, we find that iu the former only about 8 per cent of the 

 bydroids are pluniularians, while in the latter region that group is represented by about 40 per 

 cent of the known species. Marktanner-Turneretscher's work, describing a collection that may 

 fairly be regarded as cosmopolitan, 1 includes about 162 species of hydroids, 30 per cent of which 

 are pluinularians. The American hydroids have not been thoroughly worked over since the im- 

 mense accretions were secured by the Albatross, but it is extremely probable that at least 30 per 

 cent of all the species found in American waters belong to the I'lumularida-. 



Taking the average of the proportions of plumularians to other hydroids as shown by a study 

 of the Clialleitgvr report, llincks's work on British Hydroid Zoophytes, Bale's Catalogue of 

 Australian Hydroid Zoophytes, Marktanncr Turueretscher's work, and a rude estimate of the 

 American species, we tiud that about 28 per cent of the hydroids treated of in these larger works 

 are plumulariaus. 



Valuable as have been the results of the Challenger expedition, wo are not justified in depend- 

 ing upon the apparent distribution of the Pluuiularidre as indicated in the table (p. Ixviii), 

 according to which only one species of plumularian was found iu the West Indian region. This 

 table, like many of those included in the present work, does not indicate the number of hauls 

 made with the dredge in each xoogeographical region, and where only a few casts were made so 

 much depends upon the particular conditions attending each that it is impossible to derive any 

 very reliable quantitative results regarding the fauna. Where a more limited area is carefully 

 worked over, these sources of error are almost eliminated, at least greatly reduced. Over 3,000 

 hauls of the dredge, tangles, etc., have been taken by the vessels engaged in the work of the 

 United States Fish Commission and the United States Coast Survey, and by the Bahama expedi- 

 tion from the State University of Iowa. These expeditions have worked almost exclusively along 

 the Atlantic coast of the United States and in the West Indian and Nova Scotian regions as 

 defined by Allnian in his CluiUc/ii/a' report. In these regions the ClxtUciKjcr made about 55 

 hauls of the dredge, with the astonishingly meager result of only one plumularian (Streptocaulus 

 pulclierrim-us), a result probably due to the fact that most of the work done in this region was in 

 water of great depth and beyond the continental slope. 



A more thorough working of this same region by the various United States expeditious 

 resulted iu the discovery of over 100 species of Pluumlarida-, indicating in all probability the 

 richest plumularian fauna yet discovered in any part of the globe. 



As mentioned above, over 300 species of Plumularida' have been described. About 33 

 per cent of these are found iu the West Indies and off the Atlantic coast of the United States; 

 about 23 per cent in the Australian and East Indian region; about 13 per cent in the Mediterra- 

 nean and European region; the remaining 31 per cent being scattered over other parts of the 

 globe. It is worthy of note that over half of the plumulariaus are found in the two widely sepa- 

 rated regions, the West Indian and the Australian. Professor All man points out a curious coinci- 

 dence between the distribution of the bats and that of the Plumularidae, each having its most 

 notable centers in the East and West Indies. 



As a whole, it may be said that the Plumularidte reach their maximum development in species 

 and individuals as well as iu diversity of form and size of colonies in the warmer seas of the 

 globe, in which, as just noted, there are two well-marked centers, the one in the East Indian and 

 Australian region and the other in the West Indian. From these centers they are carried by 

 currents and spread along the bottom in various directions, reaching as far north as Alaska, 

 Norway, and Greenland. - It will be noted that in each of these cases, except possibly Greenland, 

 the far northern shoies are bathed by warm currents from tropical regions. In one case a species 

 of this group lias found its way as far south as the Straits of Magellan/' In an account of the 

 hydroida of Spitsbergen, 4 Marktanner-Turneretscher enumerates 73 species of hydroids, among 

 which there is not a single plumularian. 



In both the East and West Indies the physical conditions are especially favorable to a luxu- 



1 Die Hydroiileu <les k k. iiatiirhiHtiirischr.r Ilnl'innseuins. 



I have a specimen of Aijlaopheuoims <'uriiii/ii Verrill from C'auon Norman's collection (originally from the 

 Copenhagen Museum), that came from (ireenlaud. 

 3 Aylaui>lieitia p<tttii/<>ni<-<t. 

 ^Zoologiache .lahrbiiclier, VIII, Abtbeiluug fiir Systematik, 1895, pp. 437, His. 



