208 
PACIFIC SCIENCE, Vol. XVII, April 1963 
last stage, are spaced along the outer margin of 
the fifth leg. The posterior margin of the female 
genital segment is broadly rounded in some 
specimens and irregular in others. 
The male genital segment (Fig. 12/) is sim- 
ilar to that of the female although slightly 
longer; the lateral margins are, however, not 
indented in the dorsal view. Both the fifth and 
sixth legs arise from the posterior ventral lateral 
surface, adjacent to each other. Further, both 
legs are lobate, the sixth extending slightly past 
the division between the genital segment and 
abdomen. The fifth leg possesses one plumose 
setule on the outer base of the leg and two 
plumose setae on the distal end; the sixth leg is 
tipped by two plumose setules. 
The abdomen (Fig. 12/, g ) is bell-shaped 
and short; its greatest length is one-half that of 
the genital segment in the males, slightly longer 
in the females, and the greatest width is ap- 
proximately 1 V4 times the length. The poste- 
rior region of the single abdominal segment 
is broader than the anterior, the lateral margins 
are convex, and the lateral posterior margins 
are concavely tapered to the bilobed anal region. 
The frontal organ (Fig. 13/) is similar to that 
of the preceding stage although the component 
parts are less distinct. The attachment filament, 
if present, arises from a circular indentation on 
the anterior ventral surface just anterior to the 
frontal organ. In unattached forms this circular 
indentation forms a scar which is the only evi- 
dence of the attachment filament. The yolk ma- 
terial that was present in the fourth chalimus 
now appears to be completely absent. 
Only two specimens survived from the moult 
into the fifth chalimus to the moult into the 
sixth. Both of these specimens spent approxi- 
mately 24 hr in the fifth chalimus stage under 
laboratory conditions (temperature approxi- 
mately 23 C) . 
The sixth chalimus stage (Fig. 10c, d) is 
the last larval stage. Specimens in this stage of 
development were found both attached and free 
although, in contrast to the fifth chalimus, more 
frequently free. The greatest length of the ceph- 
alothorax, including the frontal region, is ap- 
proximately 1.2 times the greatest width, ex- 
cluding the marginal flanges. The frontal region 
is similar to that of the fifth chalimus. The lat- 
eral margins of the cephalothorax are broadly 
curved and are fringed with a distinct marginal 
flange. The posterior lateral corners of the ceph- 
alothorax are broadly rounded; the lateral pos- 
terior margins, outside the posterior sinuses, 
are bilobed, as in the preceding two stages, and 
consist of the rounded posterior extensions of 
the lateral regions and the sharply rounded lat- 
eral posterior surface of the median thoracic 
area. The posterior sinuses are distinct and U- 
shaped. The median thoracic area extends pos- 
teriorly slightly past the posterior extensions 
of the lateral areas. The posterior margin of 
the extension is broadly rounded in the female 
but has a flat median protrusion in the male. 
The lateral margins of the extended median 
thoracic area are continuous with the inner mar- 
gins of the posterior sinuses. The major cephalo- 
thoracic grooves are similar to those of the pre- 
ceding chalimus stage. Minor cephalothoracic 
grooves are visible on some specimens and, 
when present, extend posteriorly from the divi- 
sion between the frontal region and the cepha- 
lothorax. The lateral strengthening regions are 
proportionately larger than in the fifth chalimus 
but are similar in general shape and position. 
The free fourth pedigerous segment is short, 
its length approximately one-half the width. The 
anterior end is covered by the posterior end of 
the median thoracic area of the cephalothorax 
in the female but not in the male. The middle 
of the segment protrudes laterally, the fourth 
thoracic legs being attached to the distal end of 
the protrusion; the segment tapers from the pro- 
trusion to the narrower anterior and posterior 
ends. The division between the fourth pedi- 
gerous segment and the genital segment is dis- 
tinct although slightly irregular. 
The genital segment of the female (Fig. I2i) 
is slightly longer than wide, its greatest width 
being approximately four-fifths of the length. 
The lateral margins are broadly convex, the ante- 
rior lateral surface forming an irregular, node- 
like formation at the junction with the fourth 
pedigerous segment. The fifth legs arise from the 
lateral posterior ventral surface but do not ex- 
tend to the posterior end of the segment; these 
structures are lobate in outline and possess three 
plumose setae along their outer margin and one 
on the distal surface. The seta on the distal 
surface possesses a minute swelling on the prox- 
imal outer margin (Fig. 12/) which is absent in 
