1904 - 5 .] Free- Swimming Crustacea of Firth of Clyde. 797 
Most, if not all, of the species mentioned in Table I. appear to 
be “ residenters ” within the Clyde estuary, for, though they may 
disappear for a time, their appearance or disappearance may only 
be the result of periodic reproduction. Species are occasionally 
observed, sometimes in considerable numbers, the presence of 
which can only be explained by their having been transported 
thither by tidal or other currents. 
Notes on the Crustacea observed in the Plankton 
Samples collected during 1902. Table II. 
The Crustaceans observed in the plankton samples collected 
during 1902 comprised forty-nine species of Copepoda, four species 
of Cladocera, and two species of Ostracoda ; while the Amphipoda 
were represented by six species, the Isopoda by two, and the 
Sympoda by three; and also young forms belonging to the 
Decapoda, the Cirripedia, and various other groups. A few of 
the species were of frequent or common occurrence, but a large 
proportion of them occurred very sparingly; while several were 
observed only once, or at most only a few times, during the year. 
The number of samples examined for 1902 amounted to sixty-eight. 
In the following observations on the distribution of the various 
species, those belonging to the Copepoda, which are most 
numerously represented, will be noticed first, and the others in 
the order indicated above. 
Copepoda. 
An examination of the subjoined table (Table II.) shows, even 
more distinctly than the previous one (Table I.), that only certain 
species have a distribution more or less continuous throughout the 
year ; and of those, Calanus helgolandicus , Pseudocalanus elongatvs , 
and Acartia Clausi (Nos. 1, 3, and 17 on the table) are the most 
common. 
The Calanus was observed in each of these sixty-eight samples ; 
and on several occasions, from February till the end of June, it 
occurred in considerable abundance, but in the majority of the 
samples its numbers were more limited. Moreover, though 
it appeared to be scarcer in the samples collected in August 
