2 DEPARTMENT OF THE NAVAL SERVICE 
7 GEORGE V, A. 1917 
the relative abundance of each form by estimating the frequency with which it 
occurred. Four élasses of frequency were recognized and termed abundant, frequent, 
occasional, and rare, the last being employed when only one or two examples of a 
form were found in a sample, the other terms explaining themselves in a general 
way on this basis. In the table these terms have, for convenience, been indicated 
by the numbers 4-1, 4 standing for abundant, 3 for frequent, ete. Seasonal variations 
in the character of the plankton: are revealed in this way, and a few remarks may be 
made upon these variations and on various forms occurring in the collection so far 
as they have been certainly identified. 
THE PHYTOPLANKTON. 
Less attention was given to the phyto- than to the zooplankton, partly on account 
of the inaccessibility of the literature necessary for the identification of the forms, 
and partly because the Diatoms which form a major portion of*it have already been 
discussed by Bailey." The form occurring with the greatest constancy is the diatom 
Coscinodiscus, which is absent from but a few of the collections throughout the 
entire period which they represent. With the onset of spring, however, it becomes 
somewhat more abundant than in the winter months, behaving in this respect like 
other members of the phyto-plankton. Four different forms of the genus have been 
recognized, which, with the aid of Rattray’s Monograph” and such other literature 
as was accessible, have been identified as C. radiatus Ehr., C. concinnus W. Sm., C. 
centralis Rattray, and C. fasciculatus O’Me. The first three species have already been 
recorded by Bailey, and may be distinguished from one another and from C. fascicu- 
latus by C. radiatus being the smallest, and having distinctly coarser markings and 
no central rosette or space; by C. centralis having a central rosette, but no signs of 
fasciculation of the markings at the periphery, near which are situated asymmetric- 
ally two apiculi; by C. concinnus having a central rosette, much finer markings than 
either of the others, these markings showing indications of fasciculation towards the 
periphery, and each fasciculating line terminating there in a minme apiculus; and 
by C. fasciculatus having a central space, and the markings arranged in fasciculi, 
each of about nine radial rows, the central one of which alone reaches the central 
space, the others terminating at successively greater distances from it. 
Next in order of constancy to Coscinodiscus, though falling much behind it, 
was Biddulphia, the most frequently occurring species being b. aurita Lyngk., although 
a much larger form with small scattered chloroplasts, probably B. mobiliensis Grun, 
was also observed in several gatherings. From October, until about the end of 
February, Biddulphia was rare or absent from the collections, but throughout March 
and April it was of frequent occurrence, diminishing again rapidly in May. Its 
seasonable distribution was, therefore, similar to that of Coscinodiscus, except that 
the latter is more frequently present throughout the winter months, reaching a maxi- 
mum frequency in March and April. 
Examples of CUhaetoceras occurred at rare intervals throughout the winter, 
becoming more numerous and more constant in April, and, it may also be noted, 
occurring most frequently in the surface collections, only having been observed in 
two occasions in those of the 6-metre level. At least four or five different species 
were observed, all belonging to Gran’s sub-genus Hyalochaeta.* 
1L. W. Bailey. Some recent Diatoms, fresh-water and marine, from the vicinity of the 
Biological Station, St. Andrews, N.B., August 20-30, 1909. Contributions to Canadian Biology, 
1906-10. Ottawa, 1912. 
L. W. Bailey. The Plankton Diatoms of the Bay of Fundy. Contributions to Canadian 
Biology, 1911-14. Ottawa, 1915. 
2J. Rattray. A Revision of the Genus Coscinodiscus and some Allied Genera. Proc. Roy. 
Soc. Edinburgh, xvi, 1899. 
8H. H. Gran. Protophyta in Norwegian North-Atlantic Expedition, vii, 1897. 
