20 R. NORRIS WOLFEXDEN. 



Genital segment witli very prominent genital lubcrole, occupying half the segment, 

 (the lower half only), ilire(-teil slightly upwards in lateral aspect, with apparently three 

 lobes, an upper and lower, each large with small middle lobe, and without any eminence 

 on the upper part (of the ventral surface) of the segment as in antarctica, and also 

 invariably without the ventral liorn which is so characteristic of antarctica. In the 

 ventral aspect the genital tubei'cle appears to be obliquely placed, directed downwards 

 tow^ards the left, the vulva guarded by two prominent Haps of which the right one is 

 below the left one. The whole tubercle occupies more of the left than the right side of 

 the segment, which in the dorsal view is only slightly swollen at each side. 



The first and second pairs of feet and the number of bristles on the maxilla are the 

 same as in antarctica. 



While the female is so distinctly different from that of E. antarctica I am unable 

 to find similar distinction in the males. Both kinds appear frequently to occur together 

 in the same sample, and all the males appear to ])e alike. 



ONCE A (Giesbrecht). 



Oncea curvata. 

 Oncea curvata, Giesbrecht, 'Bclsjica' Report, p. 42. 



According to Giesbrecht, this species difiers from 0. sukilis in the following points : 

 Length, 0"6-0"8 mm., the body lengthened, the three segments posterior to the genital 

 are about as long as broad, and comparatively longer than in any other Oncea species 

 except subtilis (in which tliey are longer than broad), all three segments together are 

 shorter than the genital (in f<ubtiUs, the genital segment is only a little longer than the 

 two succeeding segments), the furca is as long or a little longer than the anal segment 

 (in subtilis shorter). The posterior antennae in both kinds are similar, the maxillipedes, 

 however, differ ; the terminal hook which, in subtilis, is thin and unarmed, is strong 

 and beset with pretty long teeth on the concave side, in curinta. The swimming feet 

 are similar in both species, except that in curvata the proximal outer marginal bristle 

 on jRi 3 occ^urs in all four pairs, while it is absent in subtilis, and the lancet-shaped 

 apical bristle of the fourth foot is in cuj^vata longer than in subtilis. 



The few examples that occur in the ' Discovery ' collections are smaller than 

 Giesbrecht's examples, none being more than "56 mm. in total length ($s with egg sacs 

 attached). 



The genital segment is a little longer than the next three segments, the furcal and 

 anal segments of the same length, the second abdominal segment as long as broad, and 

 rather larger than the third segment, the relative lengths of .Vl). 2:3:4 and furca 

 being as 4 : 3 : 4 : 4, the latter nearly three times as long as broad. 



In the posterior antennas, the first basal joint is the largest, and the inner margin 

 of the second basal has a few fine teeth ; the distal segment has three proximal bristles 



