1896. ] OF THE GENUS SERGESTES. 959 
vii. Notes on the Species in Group II. 
A. S. hensenit (Ortm.).—Of this interesting species I have seen 
only two adult specimens, lent me by Geheimrath Prof. Dr. V. 
Hensen. As the representation by Ortmann (p. 38, Taf. iii. fig. 3) 
is rather deficient, I shall add some notes. The rostrum is low 
and short; the supraorbital and hepatic spines are short. Mxp.’ 
is considerably longer than trl.* and its 4 proximal joints, though 
more slender than in the following species, are yet much stouter 
than in trl.*; the 2 distal joints are quite naked along one margin, 
the fifth almost more than double as long as the sixth, which is 
divided into 5 subjoints, the last 4 of which are equal in length, 
while the first of them is as long as the two following together; at 
the base of the first subjoint and at the apex of the first, third, and 
fifth subjoints is found a long spine; at the apex of the second, 
fourth, and fifth subjoints a spine about half as long as the long 
spines ; finally along the same margin a fine comb of very numerous 
spines about as long as the diameter of the joints; the fifth joint 
of mxp.” has about 10 longer spines along the margin and on its 
distal two-fifths a comb similar to that on the sixth joint, but its 
spines become shorter towards the base. By this singular armature 
the species is easily distinguished from all other species known to 
me. Above trl.? a large and a very small branchia, the latter of 
which is less than a third as long and bat half as broad as the large 
branchia; above trl.* two branchie, the anterior somewhat larger, 
the posteriur somewhat smaller than the small branchia above trl.’; 
thus the branchiz are very different from those in the other species 
of the group. In the following species we find a well-developed 
process on the third joint of trl.’ and a similar one on trl.?, but in 
this species the process in trl.’ is rudimentary and wanting in trl.’ 
On the ext. br. of urp. no spine is found on the exterior margin, 
and in the one specimen the ciliated part occupies three-fifths, in 
the other specimen almost four-fifths of its length. In no other 
species have I met with any similar variation in this feature, but 
it also exists in the larve (see below). 
S. sargassi, Ortmann (p. 34, Taf. ii. fig. 1), is the Mastigopus 
of S. henseni. As the material seen by me is rather incomplete, the 
larger specimens being not very large and besides defective, I add 
only a few remarks to Ortmann’s description. Mxp.’ is elongated 
and incrassated in proportion to the legs as in the adult, the fourth 
joint at the apex and just above the articulation produced into a 
large, conical process—a very good character for the species ; and 
ina larva a little more than half-grown the sixth joint was already 
divided into the 5 subjoints. In the largest well-preserved speci- 
men, 8 mm. long, I found above trl.*a large branchia and a lamella, 
comparatively somewhat larger than usual, which had begun to 
develop itself into a very small branchia, above trl.* a very small 
branchia and a simple lamella; the normal lamellz above trl.* and 
trl.’ are a little larger than usual. As in the adult the ciliated part 
on the exterior margin of the ext. br. of urp. occupies about three- 
fifths or four-fifths of its length in specimens between 4°5 mm. and 
Proc. Zoou. Soc.—1896, No, LXII. 62 
