15i 



DE. G. H. rOWLEE— BISCATAN PLANKTON : 



NOTE ON THE DISTRIBUTION OF THE MOLLUSCA. 



By G. Herbert Fowler, B.A., Fh.D., F.L.S., F.Z.S. 



The chief thing noticeable abovit the distribution of tliese species is their rarity at 

 the actual surface. Out of seventeen distinguishable forms, only three were taken 

 at the surface, and all three were more plentiful at lower horizons of the epiplankton. 



On the other hand, between 25 and 100 fathoms inclusive, despite the sparse 

 population as evidenced by the small number of total specimens, the captures were 

 niunerovis. Mollusca occurred : 



Few species occurred in sufficient numbers or with sufficient regularity to allow of 

 an accurate study of their distribution, and only one could be regarded as common at 

 the surface ; but four were sufficiently plentiful to justify an analysis of their 



occurrences 



Carinaria sp. 



At 



25 



50 



75 



100 



S g 



Below 100 fathoms it occurred in no haul of the closing-net. We may fairly 

 conclude that this form was epiplanktonic, with an optimal horizon at 50 fathoms. 



When tried on the time-depth table, there was no indication of vertical oscillation ; 

 again, when tested on a "day, night, and rain" table (compare stq)ra, pp. 60, 61), it 

 was not obvious that the distribution was affected by light, darkness, or rain. But the 

 actual numbers captured were too small to allow of certainty on this point. 



Peraclis brevispira, sp. n. 



At 



* As in previous acalj-ses, the nine hauls with a small fine-meshed net have been omitted, and the captures 

 multiplied by a time-factor (compare the second footnote on pp. 50 and 60). 



