THE WINTER PLANKTON nn 3 
SESSIONAL PAPER No. 38a 
The most frequent form was what seemed to be C. lacinioswm Schiitt with a single 
chromatophore, the foramina slightly constricted at the middle, and tke terminal 
sete marked by a delicate spiral line most easily seen in dried samples; spores were 
not observed. Somewhat less frequent was a spirally coiled form which seemed to 
be C. curvisetum Cleve, with a single chromatophore adjacent to the front of each 
frustule. C. decipiens Cleve was still rarer, but readily distinguished from the others 
by its coarser sete and the occurrence of four to six chromatophores, and a single 
example of a form with numerous scattered chromatophores, thus resembling C. teres 
Cleve, and another with two chromatophores adjacent to the ends of the frustule (C. 
constrictum Gran.?) were also observed. : 
An interesting seasonal distribution was shown by Thalasstosira Nordenskjoldu 
Cleve. Throughout October, November, and the winter months this species did not 
oceur in the collections, but on March 13 it suddenly appeared in considerable quan- 
tities. It was again taken on March 25 and 26, though not in any great numbers, 
but on April 4 it formed by far the greater bulk of the plankton, which condition 
persisted until the collections ceased at the end of May. 
Another genus that showed a distinct maximum of occurrence at the end of 
March and the beginning of April was Rhizosolenia, so far at least as its most 
frequently occurring species, R. setigera Brightwell, was concerned. AR. styliformis 
Brightwell was also observed, but only in one collection, and another form, which 
seems to be very similar to R. gracillima Cleve was also observed. This last form 
was observed on four occasions, October 16 and 20, February 26 and March 2, and 
on all occasions except the last it was found in collections made at the 6-metre level,- 
while it was absent,or at all events rare, in the surface collections made on the same 
dates and at the same stations. Whenever found it: was in great numbers. The 
frustules were long, filiform, without any siens of markings except a slight depres- 
sion close to each extremity, and were filled with small, scattered oval or circular 
chromatophores. The longest individuals measured as much as 2:2 mm., with @ 
diameter of 0-:0075 mm., and the great majority exceeded 1:0 mm. in length. These 
measurements greatly exceed those given by Cleve! in the description of the species, 
but otherwise the agreement is close. A species of Schizonema, and one of Fragilarva 
were also somewhat more abundant in the early spring months, and examples of 
other genera were occasionally observed, but no attempt was made to determine their 
exact identity. Of the genera so represented, mention may be made of Navicula,. 
Rhabdonema, Gomphonema, Bacillaria, and Campylodiscus. 
Of occasional occurrence also were certain filamentous alge, the only one that 
was identified even as to the genus, being a species of Cladophora, which, like many 
of the diatoms, showed a maximum of occurrence, its greatest frequency and con- 
stancy being in the early part of April, and being of only a few days’ duration. 
DINOFLAGELLATA. 
The most frequent representative of this group was the well-known Ceratium 
tripos (O. F. M.) Nitzsch, C. fusus (Ehr) Dujard. also occurring, though not quite 
so frequently, and (@. furca (Ehr) Dujard. was recognized in two gatherings, but 
only in very small numbers. Of the genus Peridinium, P. divergens var. reniforme 
Ehr. (P. depressum Bailey) was found occasionally, and was the only member of the 
eenus recognized. Dinophysis norvegica C. and L. was also observed, but only on one: 
oceasion. None of the Dinoflagellates occurred in such numbers as be important: 
quantitative constituents of the plankton, C. tripos only on one occasion being in 
sufficient quantity to be regarded as frequent. 
PIER ARS Cleve. On some new and little-known diatoms. K. Svensk. Vet.-Akad. Handl, xviii, 
No. 5, 1881. 
38a--14 
