20 
R. NORRIS WOLFENDEN. 
Genital segment with very prominent genital tubercle, occupying half the segment, 
(the lower half only), directed 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 horn which is so characteristic of antarctica. In the 
ventral aspect the genital tubercle appears to be obliquely placed, directed downwards 
towards 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 be alike. 
ONCE A (Giesbrecht). 
Oncea curvata. 
Oncea curvata , Giesbrecht, ‘ Belgica ’ Report, p. 42. 
According to Giesbrecht, this species differs from 0. subtilis 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 they are longer than broad), all three segments together are 
shorter than the genital (in subtilis, 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 curvata. The swimming feet 
are similar in both sjDecies, except that in curvata the proximal outer marginal bristle 
on Ri 3 occurs in all four pairs, while it is absent in subtilis, and the lancet-shaped 
apical bristle of the fourth foot is in curvata 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^arne length, the second abdominal segment as long as broad, and 
rather larger than the third segment, the relative lengths of Ab. 2:3:4 and furca 
being as 4 : 3 : 4 : 4, the latter nearly three times as long as broad. 
In the posterior antennae, 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 
