COPEPODA. 
37 
XANTHOCALANUS MAGNUS. 
(Plate VII., figs. 1-9.) 
Xanthocalanus magnus, Wolfenden, Plankton Studies, Part II. (1906), p. 32. 
? 6'0 mm. long. Head dorsally with line of separation from the first segment, 
rounded and without any trace of crest; produced in front into a chitinous lamella 
with two pointed rami. Last thoracic segment on each side a little produced. Abdomen 
short, the cephalothorax being three and a half times its length. Genital segment 
protuberant ventrally and longer than the next two, anal segment very small, and 
furcal segments much longer than the anal. 
Anterior antennas, reaching about the end of the genital segment, of twenty-four 
segments, with thick basal joints, the eighth and ninth coalesced, the last segment very 
small. Posterior antennas with Ri longer than Re, the first joint of the latter with 
strong rounded projection of the lower and inner margin. The masticatory plate of 
the mandibles with strong teeth, the two outer longer than the inner ones, which are 
short and all of the same size. Anterior foot jaws short, but strongly built, the outer 
margin very convex, the last lobe bearing a very strong thick basally and curved sickle¬ 
shaped hook, tapering distally; all the bristles of Ri represented by sensory brush and 
vermiform appendages. The posterior foot jaws somewhat extended, the first basal 
comparatively thick and with a brush appendage, the second basal elongated and thin, 
with very short marginal bristles ; Ri also elongated, the first and second joints long, 
and its bristles comparatively short. Maxillae very like the preceding species, but B 2 
with five, Ri with ten bristles, Re elongated and narrow. 
1st feet, Re with three distinct segments and three external spines ; Ri only one 
segment. 
2nd feet, Re of three broad segments very spinulose on the surface, and with short 
external marginal spines, Ri of two segments with prominent bunches of spines on the 
surface of Ri 2. 
3rd and 4th feet, each ramus of three segments, the surfaces spinulose. 
5th feet small, of three segments more or less covered, especially the last segment 
and margins, with comparatively long, spine-like bristles; the terminal segment with 
two short terminal and two very short marginal spines, not articulating. 
This is an adult female, and resembles the animal I have described as Xanthocalanus 
magnus (Plankton Studies, Feb., 1906) so closely that I think they must be regarded 
as the same animal. The ‘Gauss’ animals are, however, very much larger (up to 8’8 
mm.), but the only essential differences which I can detect are the much greater size 
of the latter, the rather more pointed dorsum of the head, and the more hirsute 
abdominal segments. In these collections I have found many examples which appear 
to differ only in size, and I am inclined to think that this ‘ Discovery ’ example is 
merely a smaller one of the same species. The 5th pair of feet are strikingly different 
from the northern species. 
