226 RITTER 



Kadiak Island. — Distaplla occidejitalis ; D. confusa; Didemmnn 

 straizgulatuni ; AmarouciuJii coei. 



Shumagin Islands. — Ascidia adhcerens ; A^naroucium californi- 

 cum; Botryllus magjttis. 



Seven species were obtained only by dredging ; and as the 

 dredge was used but little and not in depths exceeding twenty- 

 five or thirty fathoms, it seems certain that this method of col- 

 lecting, when more thoroughly applied in these waters, will 

 yield richer returns. 



The largest number of species obtained at any one place was 

 five, at Yakutat Bay, where the group seems to be better repre- 

 sented than at any other collecting station. It must be said, 

 however, that the shore collecting was carried on there rather 

 more extensively than elsewhere, and under better conditions, 

 the tides being particularly favorable at the time. 



The distribution of marine littoral animals, always a difficult 

 problem, is peculiarly intricate in the case of the Ascidians. 

 The conditions upon which their existence depends appear to 

 be more complex and delicate than for most other groups of 

 animals. 



In the course of collecting along the Pacific Coast from 

 southern California to western Alaska during the last ten 

 years, I have been repeatedly surprised at finding Ascidians 

 almost wholly absent from places apparently differing in no re- 

 spect from others where they occur abundantly. Observations in 

 Alaskan waters have, however, shown that the influence of the 

 glaciers, discharging into the sea, are there an important factor. 

 Few Ascidians were found at any point where considerable 

 glacial debris is present in the water, and where sedimentation 

 is in rapid progress. In all probability the diminished salinity 

 of the water, due to fresh water derived from melting ice, is 

 a condition unfavorable to their existence. 



Grateful acknowledgment is here made to two of my as- 

 sociates on the expedition, Dr. Wesley R. Coe and Professor 

 Trevor Kincaid, for their courteous help in collecting Ascidians. 

 Of the fifteen species obtained, eleven are here treated as new 

 to science, one of them being the type of a new genus. The 

 complete list is as follows : 



