HYDROIDS OF THE 1934 ALLAN HANCOCK PACIFIC 



EXPEDITION 



(With Fifteen Plates) 



C. McLean Fraser 



Introduction 



An invitation to accompany the 1934 Hancock Expedition on velero 

 III, to collect coelenterates, and more especially hydroids, in such an 

 extensive virgin area, w^as gladly accepted. 



In the ten vv^eeks' cruise opportunity was afforded to collect in the 

 Revilla Gigedo Islands, the Galapagos Islands (where three weeks 

 were spent), and the mainland coast from Guayaquil, Ecuador, to San 

 Diego, California. The Gulf of California was not visited. Stops were 

 made in 40 locations and collections were made at 161 stations, 104 of 

 which were dredging stations. 



In most of the area covered the sea bottom was suitable for coelen- 

 terate growth, although at times it was rough enough to make dredging 

 somewhat difficult. The coast of northern Ecuador and of Colombia, 

 adjacent to the tropical rain forests, provided the main exception. For 

 an undetermined distance off shore here the bottom is covered with 

 such a fine silt or ooze that, in places, it would not trip the bottom 

 sampler. In this area hydroids could be obtained only by dredging in 

 shallow water over the surface of the reefs running out from shore. 

 With the exception of this muddy area, less material in general was 

 obtained from the same amount of effort in the oceanic area than from 

 the mainland coast. This does not necessarily mean that the oceanic 

 fauna is less rich. There have been so few soundings recorded in the 

 oceanic area and there is so little information as to the nature of the 

 bottom that dredging is much of a speculative procedure. The Mexico 

 coast was particularly rich in hydroids. The best catch of the whole 

 expedition was obtained just east of the islands off Navidad Head, at 

 the entrance to Tenacatita Bay, where 44 species were obtained at the 

 one station. 



As the detailed geography of this region is not, in general, well 

 known, it may be wise to give here a list of the locations where collec- 

 tions were made, to avoid the necessity of giving the details in connec- 

 tion with the distribution of the species. 



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