54 THE VOYAGE OF H.M.S. CHALLENGER. 



In some gatherings the . species was extremely abundant, more especially in those 

 taken off South Australia and in the tropical Atlantic ; and the red colour (brick-red) 

 mentioned by Dana was distinctly observed in some samples, even after their prolonged 

 immersion in spirit. These specimens are undoubtedly identical with those described by 

 Sir John Lubbock as Undina longipes, and though Dana's figures are too small and his 

 detailed descriptions too meagre for absolute certainty, I can scarcely doubt that they are 

 meant to refer to this species : it would be strange if so widely spread and so abundant 

 a species had escaped him, and if so that his species^ — likewise widely spread — should have 

 also eluded the Challenger. Dana's drawing of the fifth foot of the male — the only 

 characteristic detail which he gives — applies fairly well to our specimens, if we allow for 

 the absence of minutiae, consequent, perhaps, on the use of too low microscopic powers ; 

 and I cannot recognise any distinction between the examples described by the same 

 author under the three specific names, vulgaris, simplex and inornata. 



One unmistakeable diagnostic mark of Undina longipes is the peculiar emargination 

 of the second foot in both sexes — a mark quite sufficient for specific determination, even 

 when no males may be present. The bidentate postero-ventral angle of the thorax, 

 though perhaps not always present, is, I believe, another good specific character. 



2. Undina darwinii, Lubbock (PI. XVI. figs. 1-4, 6-14). 



Undina darwinii, Lubbock, On some Oceanic Entomostraca collected by Captain Toynbee, Trans. 

 Linn. Soc, vol. xxiii. p. 179, pi. xxix. figs. 4, 5. 



Cephalothorax rounded off in front and behind, posterior ventral angle slightly 

 exserted. Anterior antennae of the female (figs. 3 and 4) twenty-five-jointed, the joints 

 not varying much in length, except that the second is much larger than the rest ; in the 

 male (fig. 2) the antenna is twenty-two-jointed, angulated at the sixth joint, the first 

 two joints long, equalling the following three or four joints ; in both sexes the anterior 

 antennae are slightly longer than the cephalothorax, and clothed with marginal hairs which 

 are very short except at the apex ; the second and sixth joints, in the male, each bear a 

 single long seta. The posterior antennae have the two branches nearly equal in size 

 the inner branch four-jointed,, with two small and rather indistinct median joints. 1 

 Mandibles broad at the apex (fig. 6), numerously and sharply toothed ; basal 

 joint of the palp very large, first joint of the inner branch swollen, both branches 

 short and bi- articulate. Maxilla (fig. 7) well-developed, anterior foot-jaw small 

 (fig. 8), posterior (fig. 9) well developed. The outer branches of the swimming- 

 feet are more or less strongly serrated between the last two marginal spines ; the 



1 Fig. 5 pi. xvi. belongs to another species, and has been inadvertently included among the figures of Undina 

 darwinii. 



