174 



MOLLUSCAN LIFE ON THE SOUTH DOGGER BANK. 



By Guy C. Eobson. 

 (Published by permission of the Trustees of the British Museum.) 



Bead 12th January, 1923. 



These notes are based upon observation made while on a cruise 

 in the Fisheries Eesearch steamer " George Bligh " (Captain W. H. 

 Stewart) from 31st May to 7th June, 1922. The main purpose of the 

 survey was to take bottom samples on an intensive scale over an 

 area of 340 square miles north-east of " the South-West Patch " 

 at the south end of the Dogger Bank. Full details of this work are 

 to be published by Capt. F. M. Davis, of the Ministry of Agriculture 

 and Fisheries, as well as an account of the technical methods 

 employed. 



In the area in question, and at an average depth of 12 fathoms, 

 the bottom was found to consist almost exclusively of very fine 

 grey sand. Occasional patches of coarse and fine gravel are found, 

 as well as a little grey clay. One la!rge boulder, probably ice- 

 transported, of Scandinavian origin, was brought up. In accordance 

 with the fine sandy bottom and the depth, there was a complete 

 absence of macroscopic plant life. Practically the whole of the bottom 

 over this area is covered by a layer of shell-fragments, the significance 

 of which will be discussed later. 



The bottom was sampled at stations a mile apart, and intensive 

 work at closer intervals was undertaken. The instrument employed 

 was a large-sized Petersen " grab ", capable of covering ^ sq. metre. 

 Criticisms of this instrument and its gear may be found in 

 Captain Davis' paper. For the present purpose it may be said that 

 it appears to give a fair sample of the bottom, though the following 

 criticisms may be put forward. In the first instance it is uncertain 

 whether it gets up all the mollusca [e.g. large examples of Ensis) 

 that burrow below the surface layer of the bottom. In the second 

 place, if anything (a stone or shell, for example) happens to get fixed 

 in the teeth of the closing edges, the latter are kept slightly apart, 

 and a certain amount of the fine material is washed out of the grab. 



The following is a list of the Molluscan forms obtained : — 



Gastropoda. 



Living. Empty shells. 



Natica alden,¥oThes. Aporrhais pes-pelecani (Linn.). , 



„ catena (Da C). Epitonium communis (Lamk.). 



Bittium reticulatum (Da C). Bitcciniim undatum (Linn.). 



Propebela turricula (Mont.). Bullinella cylindracea (Penn.). 



Buccinum undatum, Linn, (egg capsules). 

 Eolis sp. 



SCAPHOPODA. 



DentaUum entale, Linn. 



