THE CIL^TOGXATHA. 



79 



I can find no distinction between this species and Aida/s jxtcijica except in tbe corona, 

 which in pacifica is confined to the trunk, and in snhtilis extends also on to the head. 

 As, however, it was not figured by Grassi, and is only one ou.t of several characters, it 

 seems fairly safe to put the two species together. The teeth are not always so numerous 

 as Grassi's niimber of 18, nor does the head look large unless the cheeks are thrown out 

 and the jaws turned in, in the death contraction. 



Distribution. — This species was comparatively scarce. It failed altogether at the 

 surface and 25 fathoms, and was taken only six times in all (13 per cent.) at 50, 75, and 

 100 fathoms. It failed in all the closing-nets, but appeared in hauls with open nets at 

 200, 250, and 300 fathoms. The only positive evidence therefore of its distribution 

 points to its habitat being between 50 and 100 fathoms; but the species being so scarce 

 in the locality, too mucU weight must not be laid upon this. 



General EyEMAUKS on the A^ertical Distribution *. 



In handling the captures as a whole, the hauls with open tow-nets can be compared 

 together with fair accuracy, and the hauls with the mesoplankton nets are similarly 

 comparable amongst themselves. But while the former were lowered to a set depth, and 

 towed horizontally at that level for a fixed time (generally an hour), the mesoplankton 

 closing-net was opened at the lowest depth and drawn up vertically through a compara- 

 tively small quantity of water before closure t. 



The mesoplankton net therefore cannot be expected to capture so many specimens as 

 the open nets used at higher levels. At the same time the hauls were so numerous, that 

 only rare species can have uniformly escaped. 



In the following tables, therefore, all hauls which could be usefully compared have 

 been divided between the open nets and the closing-nets. 



i. Hauls with open uets. 



At 





 25 

 50 

 75 



100 

 150 

 200 

 250 

 300 

 350 



o 



n 



16 



12 



13 



11 



22 



1 



1 



2 



1 



1 





tw 



d 



>a to 

 2 « 



£ 2 

 cw 



CD 



09 



o 



B 



D 



10-5 

 4-3 

 18-3 

 21-9 

 40-0 

 210 

 120 

 50-5 

 370 

 330 



* As in dealing with serratodenlata and furcata above, nine hauls with a small-mouthed net and 180 meshes 

 per linear inch have been omitted from the following calculations. The captures in all open nets have been treated 

 with a time-factor to bring them to the standard one-hour haul. The captures by the closing-net towed through 

 250 fathoms have been divided by 2-5, and through 500 fathoms by 5, to bring them to the standard lOO-tathoni 

 haul. 21 n (open for 50 fathoms only) and 21 a (a closing-net which arrived open at the surface, a miss-fire of the 

 gear) have also been omitted as not being in line with the other mesoplankton hauls. 



t Compare supi-ii, p. 4. 

 SECOND SERIES. — ZOOLOGY, VOL. X. 13 



