MAEINE BIOLOGICAL STATION AT PORT ERIN. 27 



froru wandering forms in their method of competition. 

 However Miss Thornely finds that in most gatherings of 

 Polyzoa the species are less than twice the number of 

 genera, while in our " Fauna " the average recorded number 

 is 2" 5 species in a genus. Moreover the colonies on dead 

 shells or on stones are generally not only distinct species, 

 but also distinct genera. As many as ten genera are 

 sometimes represented by the Polyzoon colonies on one 

 shell. We are accumulating further statistics on all these 

 points. 



The Submarine Deposits. 



In last year's report the nature of the deposits forming 

 on the floor of the Irish Sea was discussed in a preliminary 

 manner. During this season's work the bottom brought 

 up on each occasion has been carefully noted and a sample 

 kept for future study in the Jermyn Street Museum. 

 One point which this collection of deposits from com- 

 paratively shallow shore waters seems to bring out is that 

 the classification of submarine deposits into "terrigenous" 

 and "pelagic," which was one of the earliest oceanographic 

 results of the "Challenger" Expedition, and which is 

 still adhered to in the latest " Challenger " volumes as an 

 accepted classification, does not adequately represent or 

 express fully the facts. Terrigenous deposits are supposed 

 to be those formed round continents from the waste of 

 the land, and are stated to contain on the average 68 per 

 cent, of silica. Pelagic deposits are those formed in the 

 open ocean from the shells and other remains of animals 

 and plants living on the surface of the sea above, and 

 they are almost wholly free from quartz particles. 



Ordinary coast sands and gravels and muds are un- 

 doubted terrigenous deposits. Globigerina and Radiol avian 

 oozes are typical pelagic deposits. But in our dredgings 



