BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 97 



immigrants of recent standing can not be stated. We have no satisfactory evidence 

 that such is the case. 



The Canadian list prepared by Whiteaves includes 66 Hydrozoa, 5 Scyphozoa, 44 

 Actinozoa, and 4 Ctenophora. Of these, 41 Hydrozoa, 2 Scyphozoa, 4 Actinozoa, and 

 4 (all) of the Ctenophora are common to our Woods Hole list. It is interesting that 

 while the number of hydroids in the Canadian list is only half as great as in our own, 

 the number of actinians is about three times as great. 



The catalogue for Plymouth includes 121 Hydrozoa, 8 Scyphozoa, 34 Actinozoa, 

 and 3 Ctenophora. Of these, 34 ( + 6?) Hydrozoa, 2 (?) Scyphozoa, (2 + 1 ?) Actinozoa, 

 and 2 Ctenophora are known to be common to the Woods Hole region. 



The list of Herdman for the Irish Sea comprises 129(4- 1 ?) Hydrozoa, 6 Scyphozoa, 

 24 Actinozoa, and 4 Ctenophora. There is a rather close agreement between the 

 Woods Hole, Plymouth, and Irish Sea lists in respect to the number of Hydrozoa 

 comprised. On the other hand, both of the latter lists agree in including a considerably 

 greater number of actinians than have been recorded from the Woods Hole region. 



For the Gulf of Trieste, Graeffe catalogues 64(4-2?) Hydrozoa, 9 Scyphozoa, 29 

 Actinozoa, and 5 Ctenophora. 



In all these comparisons the differences in area and in bathymetric range among 

 the various regions must of course be kept in mind (see p. 87). 



On the average 1.8 species of coelenterates were recorded for each of the 458 regu- 

 lar stations of the Survey. The species found to be of most general occurrence was the 

 ooral Astrangia daruz, which was encountered at 158 of the stations, this being the only 

 ccelenterate which was so prevalent as to be recorded from one-fourth of the stations 

 dredged. It is likely, however, that Hydractinia echinata was actually present in at least 

 one-fourth of the dredge hauls, and that it was frequently overlooked by us in listing 

 the species in the field. 



Referring to the table on page 78, it will be seen that on the average nearly three 

 times as many species of hydroids per dredge haul were recorded for the Fish Hawk 

 stations in Vineyard Sound as for those in Buzzards Bay, while the average number of 

 Actinozoa was the same in both bodies of water. The Phalarope stations in Vineyard 

 Sound likewise show an excess of hydroids as compared with the stations in the Bay. 

 From the table on page 79 it is evident that there is a greater wealth both of hydroids 

 and of actinians on bottoms of gravel and stones than upon bottoms of mud or of 

 pure sand. As respects Hydrozoa, the average number of species is nearly twice as 

 great upon sandy bottoms as upon muddy ones. The distribution of most coelenterates 

 upon the local sea floor is, we believe, almost wholly conditioned by the character of 

 the bottom. 



Charts have been prepared showing the distribution, in local waters, of 10 species 

 of Hydrozoa and 3 of Actinozoa. A list of these, with a statement of the geographical 

 distribution of each is given below. Owing to the probable incompleteness of our 

 earlier records for the Hydrozoa, the practice of basing our charts upon the original 

 dredgings of the "regular" series only has not been adhered to for this group. The 

 results of various supplementary dredgings (see p. 62') have been incorporated here 

 as in the case of the Foraminifera and the Bryozoa. 

 16269 — Bull. 31, pt 1— 13 7 



