1904-5.] Free-Swimming Crustacea of Firth of Clyde. 
795 
occasions — three times during April and once in May. Para 
pontella brevicornis, though occasionally found in the open sea, is 
more truly a littoral species. 
Acartia Clausi , Giesbrecht, was absent from only one of the 
samples examined in 1901 ; its seasonal distribution resembled 
that of Centropages hamatus , being more plentiful during April, 
and becoming subsequently rather scarcer. 
Oithona similis , Claus, was observed only once during April and 
May, but occurred more frequently during the following months, 
and is recorded as abundant in the sample collected on 31st July, 
in Balloch Bay. 
The following species were noticed only once or at most twice 
in the twenty-nine samples examined, and very few specimens at most 
were obtained. Cyclopina littoralis was only observed in the sample 
collected on 14th May. Dactylopusia tisboides in that collected 
on 5th June. Dactylopusia Stromi on 22nd May. Diosaccus 
tenuicornis was obtained in the two samples collected on 18th 
and 31st July. While Tigriopus fulvus , of which only one or 
two specimens were observed, occurred in the same sample with 
the Diosaccus. Another species, Harpacticus chelifer , closely 
allied to the one last mentioned, was observed in several of the 
samples collected during April and May, but only in one of those 
collected subsequently. 
These Copepods are all more or less demersal in their habits, 
and therefore, though sometimes common in gatherings from the 
bottom, they are not often present in plankton collections. 
(2) The Cladocera. 
This suborder of the Crustacea was represented in the collection 
for 1901 by Evadne Nordmanni, and by three species of Podou , 
viz., P. polyphemoides, P. intermedins, and P. Leuckarti. The 
Evadne occurred in most of the samples examined, but appeared to 
be rather more frequent in those collected after the end of May. 
Podon polyphemoides and P. intermedius were only noticed in the 
samples collected in July ; while P. Leuckarti , on the other hand, 
was present in all of those, save two that were collected during 
April, May, and June, but was absent in all the others; this seems 
