168 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 4 



Although the list of species in the region under consideration is very 

 far from being complete, especially as most of the material was taken 

 from the shallow water not very far from shore, it is quite possible that 

 these species may be quite representative, because the stations for col- 

 lecting were selected with considerable care, at not too distant intervals. 

 The most noticeable gap is that between Costa Rica and Mexico on 

 the Central American coast. Although this is so, the region is so large 

 and the spots touched so almost insignificantly small that the distribution 

 records are necessarily very much scattered ; thus it is not possible to 

 draw general conclusions as to distribution routes with any degree of 

 satisfaction. The series of five distribution tables supports and empha- 

 sizes this statement, but still the tables are of interest because they show 

 the trends in many of the species, genera, and even in some of the 

 families. It is scarcely worth-while to remark on these trends in detail. 

 A few instances will suffice to indicate their nature. 



Of the 213 species listed in Table I, 94 species have been described 

 as new, 119 were previously recorded. Much the greater number, 152, 

 was obtained from Division C, 71% of the total number, with the other 

 two divisions more nearly equal; Division A with 92, 43%, and Di- 

 vision B with 83, 39%. Of the total number 30 were found in each of 

 the three divisions. Besides these, 23 were common to Divisions A and 

 C, 27 to B and C, but only 4 to A and B. Since the number common 

 to A and B, not found in C, is almost negligible, it is reasonable to 

 suppose that Division A has received the 30 species common to the three 

 divisions through Division C rather than through Division B. 



Of the species listed, only 15 have been reported south of Peru, and 

 all but three of these have also been reported from the Northeast 

 Pacific, the North Atlantic, or both. It would seem that there is quite 

 an effective barrier to hydroid distribution where the Humboldt Current 

 leaves the South American coast to pass westward into the Pacific. 



There is no indication of any similar barrier north of the equator. 

 Of the 66 species in the list (55% of the 119 species previously re- 

 ported) also recorded from the Northeast Pacific, 36 appeared in 

 Division A and 61 in Divisions B and C. Of the latter, 12 were re- 

 stricted to the west coast of Lower California, 10 others reached the 

 Gulf of California, 7 to the mainland of Mexico, 1 to Costa Rica, 8 

 to Panama, and 23 were obtained farther south, in Division B. The 

 detailed distribution is shown in Table III. 



