180 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.4 



of the additional distribution data. So many species, described previously 

 from only one location, and hence of which practically nothing could be 

 learned as to their distribution, have appeared again in this collection, 

 some of them many times, and in so many species, the known distribution 

 range has been much extended, or gaps have been filled, so that the clarity 

 of the distribution picture has been sensibly increased. 



In spite of all these additional records, there are still 47 species with 

 but one distribution record each. Hence although the distribution picture 

 is much clearer than previously, much more collecting must be done 

 before it is anywhere near being wholly satisfactoiy. 



In this collection, 274 species were identified, as compared with 212 

 in previous Hancock collections; 142 species were common to both lots, 

 little more than half the number in this recent collection. At present, 

 therefore, 344 species of hydroids have been identified from the Hancock 

 Pacific collections. Of the 37 species reported from the Hancock collec- 

 tion in the Caribbean Sea, 23 have appeared in the Eastern Pacific as 

 well. The 14 not reported from the Eastern Pacific, added to the 344 

 species from the Eastern Pacific, give a total of 358 species thus far 

 identified in the Hancock collections. 



Now, 464 species of hydroids have been reported from the Eastern 

 Pacific from Peru northward as compared with 435 from the northwest 

 Atlantic. (To this number should be added another species, Cordylophora 

 lacustris Allman, not before this reported from the Eastern Pacific area. 

 Some excellent specimens were collected early in this year, 1946, by Dr. 

 Robert C. Miller, California Academy of Sciences, in Lake Merced, 

 Oakland, California. This increases the number to 465.) 



The paper is prepared on the same general plan as paper No. 1, witli 

 the same treatment of synonymy, etc. In the matter of illustrations, 

 natural size figures of new species have been included as they have been 

 for all species in the Pacific and Atlantic hydroid papers, since system- 

 atists in general seem to find such illustrations useful in diagnosis. The 

 enlarged drawings, unless otherwise indicated, have the same magnifica- 

 tion, 20 diameters, so that they can readily be compared with previous 

 illustrations. So little literature has been cited that is not included in 

 earlier citations, especially in paper No. 1, that it is not worth while to 

 include a complete bibliographic list for this paper. 



As previously, I must pay tribute to the University of Southern 

 California, to Captain Allan Hancock, as Captain of the Velero III, 

 with the various scientists aboard, who have assisted in getting collections 

 together, to all the officers and men of the ship's company at various 



