1904-5.] Free- Swimming Crustacea of Firth of Clyde. 
803 
exceptions, observed only in April and May ; but young Decapoda 
appeared to be more generally distributed. One other point of 
interest in connection with the distribution of the larval forms is 
that minute organisms, generally known by the name of Microniscus i 
which at times are found adhering to Calanus , Pseudocalanus , and 
other free-swimming Copepods, were sparingly observed during the 
first three and the last three months of the year. 
These Micronisci are now considered to be the larvae of parasitic 
Isopoda which live in their adult stages in the higher Crustacea, 
as, for example, on various hermit crabs, shrimps, etc. The occur- 
rence of these larvae during the early and later months, and their 
apparent absence during summer, seems to indicate that the pro- 
pagation of these parasites takes place chiefly during the months 
from October till March. 
Notes on Plankton Samples collected outside the “ Cumbrae 
Islands ” Area in 1902. 
In 1902 a few plankton samples were submitted for examination, 
which had been collected outside the Cumbrae Islands area. 
These samples — seven in number — were collected in April, May, 
and September, but chiefly during the latter month. Three were 
collected in Ettrick Bay, on the west side of the Island of Bute ; 
and the others at different places off the Island of Arran, two 
being from Loch Ranza, one from Mauchrie Bay, and one from 
Brodick Bay. 
Twelve species of Crustacea were observed in these samples ; 
nine of the species belonged to the Copepoda and three to the 
Cladocera ; a few young Decapoda, Isopoda, Balani, and perhaps 
one or two larval forms, were also noticed. 
The following are the species that were of most frequent 
occurrence, viz. : — Calanus helgolandicus , Claus ; Pseudocalanus 
elongatus , Boeck ; Centropages hamatus (Lilljeborg) ; Temora longi- 
cornis (0. F. Muller) ; and Acartia Clausi, Giesbrecht. These 
five species were present in all the samples. The Calanus was 
abundant in the sample collected in May, but only sparingly 
represented in the others ; Pseudocalanus , on the other hand, was 
common in four of the samples collected in September ; Centro- 
