176 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



obtained. It must be borne in mind that Hargreaves' list is a 

 collation based upon many collectors' results, and covering a long 

 period. But comparison with the results of previous cruises on the 

 Bank will make it clear that this particular area is extremely poor 

 in Molluscan life. In 1875 Leckenby and Marshall obtained no less 

 than sixty-four Gastropod and fifty-seven Lamellibranch species. 



As to the gear used on the present trip I am satisfied that, with 

 the two slight criticisms noted above, it obtains a fair sample of the 

 bottom, and one probably much better than that given by dredges 

 of an older pattern. 



In addition to the relatively small number of species, we have 

 to record that with one exception the number of individuals 

 obtained was very small as compared with other records. Spisula 

 suhtruncata was found locally in vast quantities. Venus gallina, 

 Mactra stultorum, Tellina fabula, and Donax vittatus were fairly 

 plentiful, but were very often represented by only one or two 

 examples of each per haul. Of the Gastropoda, Natica alderi was 

 fairly numerous, but relatively to the Lamellibranchia was scanty. 

 The others were only occasionally found. Full details, with the 

 numerical data, of the occurrence of these forms will be given in 

 Captain Davis' paper. 



The chief facts so far arrived at are therefore : (1) the general 

 poverty of molluscan life ; (2) the abundance of one form, 

 Spisula suhtruncata ; (3) the greater frequency of Lamellibranchia. 

 That the general vital conditions are not inimical to invertebrate 

 life is apparent from (a) the abundance of S. suhtruncata, (6) large 

 hauls of Hydralmannia taken at two stations, (c) the plentiful and 

 varied population of the quartzite block referred to previously. 



In discussing the relations between the mollusca of the South- 

 west Patch and their environment, and initiating comparisons with 

 previous results, one is under a certain disadvantage, in that previous 

 workers did not record the type of bottom on which the various 

 forms were obtained. We do not know, therefore, whether the 

 previous hauls, such as that of Leckenby and Marshall, were obtained 

 from a bottom similar to that explored on the cruise now described. 



It is not easy to account for the poverty of molluscan life in this 

 area. We may refer the absence of Gastropoda to the sandy bottom, 

 though the Naticas which are specially adapted for life in such a 

 place can scarcely be called plentiful. On the other hand, that 

 such a sandy bottom is not wholly a deterrent to other Gastropoda is 

 shown by the fact that Propehela and Bittium were found alive there. 

 I believe it is generally agreed that the Prosobranch foot is not well 

 adapted to crawling over fine loose sand bottom. But I do not 

 think this is wholly true, as I have found Littorina occasionally, 

 and species of Paludestrina frequently, living on a bottom of fine 

 suspended sand, and even mud. I therefore feel that the power of 

 effecting progress on the bottom is not wholly the determining 



