HALIPORUS THETIS. 193 
a low keel. The inferior keel gives off a branch from its lower or external 
side, near the posterior border of the carapace. There is, besides, an inferior 
submarginal keel running from the branchiostegal spine back to the hind 
border of the carapace. The several fields or areas included between the 
grooves and carine above mentioned are more or less rough with corrugations 
of the integument. 
All the segments of the abdomen are carinated along the median dorsal 
line. Their pleure are shallow and rounded. On each side of the segments 
is seen a longitudinal furrow, whose edges tend to rise into carine. This 
furrow is most emphatic on the fifth and sixth segments. The sixth seg- 
ment is once and a quarter as long as the fifth segment, but only two 
thirds the length of the telson, which is armed with a pair of conspicuous 
lateral spines near the tip and about four pairs of very minute spinules on 
the margin in front of them. 
The ophthalmic peduncles are one half as long as the rostrum. On their 
inner side is borne a small tubercle. The eyes are large, black, broader than 
their peduncles. The basal segment of the antennule is armed on the ex- 
ternal margin with two small spines, one near the middle, the other at the 
distal end; the second segment is nearly twice the length of the succeeding 
one, hairy, with both the inner and outer edges of its upper surface raised 
into visible carine ; the flagella are lost in the single specimen examined. 
The basal segment of the antenna is equipped with an external spine 
directed downward and forward; the scale is longer than the antennular 
peduncle, rather broad, thin and membranaceous in texture. The tips of 
the third maxillipeds when extended forward reach beyond the distal end 
of the antennal scale ; the carpus joint is expanded, and flat on its inner sur- 
face. The third pair of legs reach forward about as far as the third maxil- 
lipeds. The last pair of legs, although rather short for the genus, reach 
forward beyond the distal ends of the third pair; the merus and carpus are 
of equal length, the propodite half the length of the preceding segment, and 
curved. The dactylus is one half as long as the propodite. The exopods 
of the third maxillipeds are small, and throughout the series of legs these 
organs are so small that they may be considered rudimentary. There are 
rudimentary podobranchial plumes, discernible by the aid of a lens, attached 
to the epipods of the third maxillipeds and the first three pairs of legs.” 
* According to Spence Bate, there are rudimentary branchial plumes attached to the epipods of the 
third maxillipeds and the first pair of legs in the genus Haliporus. In H. nereus and H. doris (as in Hyme- 
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