COPEPODA. 37 



XaNTHOCALANUS MAGNUS. 



(Plate VII., figs. 1-9.) 

 Xanthocalanus magnus, Wolfenden, Plankton Studies, Part II. (1906), p. 32. 



9 GO min. long. Head dor.sally 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 antennae, 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 antennae 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 a23peudages. 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 spiuulose 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 descrilied as XaiUhocalanus 

 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.), l)ut 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. 



