THE WINTER PLANKTON 5 
SESSIONAL PAPER No. 38a 
C. Ehrenbergi, var. subannulata, except that the turns of the spiral are much fewer. 
The length of the “house” was 0-26 to 0-34 mm., with a diameter at the mouth of 
0.7 to 0-8. 
PORIFERA AND COELENTERA. 
What were taken to be sponge spicules were observed in a number of gatherings, 
usually associated with annelid sete. Their occurrence is sufficiently indicated in 
the table. Of Coelentera, the empty cups of Campanularian hydroids were occasionnally 
observed associated with Crustacean exuvie, and on October 29 and in the last collec- 
tions that were made (May 29) a few examples of Anthomeduse were observed, but 
unfortunately in a condition very unfavourable for certain determination. 
ECHINODERMATA. 
Throughout the winter, no representatives of this group were taken, but at the 
end of April and beginning of May a few Plutei were obtained which could not be 
satisfactorily identified. On April 6, a considerable number of ova in various stages 
of segmentation up to the blastula stage were found. They were somewhat opaque, 
and inclosed within a thin structureless membrane. They were taken also on April 
10, and with them were then associated larve which could be recognized as belonging 
to some species of Holothurian. The general appearance of the ova and younger larveze 
make it exceedingly probable that they were younger stages in the development of the 
same form. The larve continued to be taken through April and May, and were a 
quite characteristic feature of the plankton during these months. 
Two Holothurians occur at St. Andrews that may be the producers of these ova, 
Cucumaria frondosa Gunner, and Lophothuria fabricti (Dub and Kor). The former 
is the more common, but the fact that the ova and larve have, when alive, the same 
brilliant scarlet colour that makes Lophothuria fabriciit so conspicuous, suggests that 
they may be the product of that species. ~ 
ANNELIDA, NEMATODES, ROTIFERS, AND CHAETOGNATHA. 
Examples of all these groups were observed, but never in such numbers that 
they could be regarded as important elements of the plankton. 
Sets of various forms which evidently were from Annelids were found in fair 
numbers in several gatherings taken after March 1, but of more importance was the 
occurrence of Annelid larve during April and May, never in any great numbers in 
any gathering, but sometimes reaching the grade of frequency indicated in the table 
by the term “ occasional.” It was not possible to identify the form which produced 
the larvee, but from their general appearance it seems probable that they represent some 
Spionid form. 
Small Nematodes were occasionally observed in small numbers in the spring 
gatherings, but no attempt was made to identify them. The same remark applies to 
the Rotifera, which were much rarer than might have been expected. Of the Chaetog- 
naths the only form identified was Sagitta elegans which was taken January 1, the 
identification of some smaller forms taken October 29 remaining uncertain. 
MOLLUSCA. 
A few veligers were observed, but so rarely that they have not been included in 
the table. The peculiar egg-capsule, probably Molluscan, having the shape of a broad- 
rimmed hat, which Wright described from Canso, occurred at intervals throughout 
the season, and sometimes in considerable numbers. Most frequently only the brown 
empty cases were found, though occasionally those containing developing ova were 
obtained. 
