438 ME. R. GUllNEY ON TBE CRUSTACEAN PLANKTON 
The description given by Norman and Scott is not altogether complete, 
inasmuch as no mention is made of the peculiar markings on the integument, 
which are quite distinctive, and the allusion to the sw-imming-feet as being 
similar to those o£ C. vernalis is misleading. It seems therefore advisable 
to supplement their description to some extent. 
The most characteristic feature of the species is the very pronounced 
crenulation of the margins of the abdominal segments and (to a less extent) 
of the last thoracic segment. The surface of the integument of the thorax 
is marked by delicate stripe which give it the appearance of being minutely 
wrinkled, while the surface, both dorsal and ventral, of the abdominal seg- 
ments is either striated or ornamented with lines of minute pits similar to 
those found in C. diaphanus. These [lits seem to run, at least on the dorsal 
surface, on the crest of low ridges, which can be distinctly seen in side view. 
The furcal rami are provided, as in C. viridis, with cilia on their inner 
margins, but these cilia are in groups and do not form a continuous 
fringe. Usually the anal operculum is very prominent. 
The swimming-legs differ markedly from those of C. vfi.rnalis not onl}'- in 
their more robust form, but also in the number of spines and setse on the 
terminal joint of the outer ramus (see Table 9). But C. vernali.i is subject 
to some variation in respect of the number of spines, and it is not unusual to 
find individuals with a spine-like formula of 3. 4. 4. 4. as in C. venustus ; but in 
these cases the number of seta3 is not increased. C. vernalis also resembles 
C. venustus in frequently having the cuticle of the abdominal segments 
pitted. The two species are, however, quite distinct, the form of the f urea 
alone sufficing to distinguish them, apart from the differences in the form of 
the swimming-legs and the excessive pitting of the cuticle in C. venustus. 
The resemblance to C. capillatus, Sars, is somewhat closer. The antennre 
are 12-jointed in each species ; the form of the receptaculum and the 5th leg- 
is closely similar, and the spine- and seta-formula of the legs is identical. 
On the other hand, the legs of C. capillatus are distinctly more slender, and 
the furcal rami much more elongated and smooth on their inner edge. 
Further, though the abdominal, segments show a slight toothing of the 
posterior margins, this is not pronounced, and I have not been able to detect 
any surface pitting in specimens from Norway which I collected many years 
ago in the Romsdal. 
There remains for comparison the species described by Graeter in 1908 
under the name of C. erinitus. M. Chappuis has been kind enough to send 
me a mounted specimen of this species, and an examination of this specimen 
and of the published descriptions of Grraeter and Chappuis convinces me that 
the two species are identical. They agree in the following characters, 
wherein they differ from most other species : — 
(1) Antennule of 12 joints. 
(2) Furcal rami short, slightly divergent, with groups of cilia on their 
inner edge. 
