202 
convex and extends between the apices of the 
posterior sinuses. The eyes are similar to those 
of the preceding stages and are situated in the 
anterior one-third of the cephalothorax. Cepha- 
lothoracic grooves are indistinctly present or 
absent although some irregular dorsal grooves 
are usually present in the anterior part of the 
body. 
The free second pedigerous segment is much 
wider than in the copepodite, being more than 
3 times as wide as long. The lateral margins are 
smoothly convex, the posterior margin flatly 
convex. The free third pedigerous segment is 
approximately 2 Vi times wider than long, the 
posterior end is narrower than the anterior, the 
lateral margins are flatly convex, and the pos- 
terior margin is flat. The third thoracic legs are 
now present, the spinelike processes of the co- 
pepodite being absent. The fourth pedigerous 
segment is shorter than the third, the width is 
slightly more than twice the length, and the 
posterior region projects laterally slightly at the 
junction of the now present fourth thoracic legs. 
The posterior margin of the segment is indis- 
tinct and irregular. 
The combined genital segment and abdomen 
(Fig. 12 b), that form the fourth free segment, 
are similar in both shape and measurements to 
that of the copepodite. 
The frontal region (Fig. 13£) is slightly ir- 
regular; the rostrum of the copepodite is absent. 
The frontal organ consists of two lobate proc- 
esses at the base of the frontal filament, an ad- 
ditional two lobate processes attached to the 
posterior surface of the first two, and an irreg- 
ular indistinct area posterior to the second set 
of processes. The frontal region is not distinctly 
separated from the cephalothorax although an 
indistinct groove is present on the ventral sur- 
face, extending from the lateral margin, in the 
region of the antennules, posteriorly and then 
across the ventral surface. 
The first chalimus stage lasts for approxi- 
mately 40 hr (based on two specimens kept at 
room temperature, approximately 23 C) at 
which time the specimens moult into the more 
elongate second chalimus. 
The general shape of the second chalimus 
(Fig. 9 a, b) is similar to that of the first chal- 
imus. The cephalothorax now includes the sec- 
ond pedigerous segment in addition to the first. 
PACIFIC SCIENCE, Vol. XVII, April 1963 
Late in this stage, however, the division be- 
tween the cephalothorax and the third pediger- 
ous segment becomes indistinct (Fig. 9b). The 
greatest length of the cephalothorax, including 
the frontal region, is approximately IV 2 times 
the greatest width, considerably longer than the 
cephalothorax of the first chalimus. The increase 
in length is presumably due to the inclusion of 
the second pedigerous segment in the cephalo- 
thorax. The anterior margin of the cephalo- 
thorax is broadly rounded except for the median 
protrusion of the frontal filament; laterally, the 
margin turns posteriorly sharply, then flares 
slightly to the lateral cephalothoracic margins. 
The lateral margins are wavy in some specimens 
and smooth in others although the entire mar- 
gin is generally convex. The posterior cephalo- 
thoracic margin is four-lobed in the early second 
chalimus, with two large lobes in the lateral 
region of each side. In older specimens of this 
stage, in which the division between the cepha- 
lothorax and the third pedigerous segment is 
indistinct, the inner two lobes are not visible 
and the median cephalothoracic area, the third 
pedigerous segment, projects well past the lat- 
eral areas. The posterior sinuses are distinct as 
two small, V-shaped depressions between the 
two lobes in the younger specimens and between 
the inner margin of the lateral areas and the 
outer margin of the median cephalothoracic area 
in the older specimens. Thus far then, the pos- 
terior sinuses appear to be due to the unequal 
growth of the lateral and medial regions of 
the cephalothorax. The dorsal cephalothoracic 
grooves are indistinct, consisting of a single, 
very short groove extending anteriorly from the 
apex of each of the two posterior sinuses. 
The third pedigerous segment, free in the 
early second chalimus, tapers evenly from the 
junction with the second pedigerous segment 
to the junction with the free fourth pedigerous 
segment. The greatest length of the segment is 
approximately four-fifths the greatest width and 
about one-fifth that of the cephalothorax. The 
free fourth pedigerous segment flares outward 
from the junction of the third to the attachment 
of the fourth legs, at the posterior end of the 
segment. The greatest width of the segment is 
approximately 1.6 times the greatest length, 
slightly more than one-half that of the third 
pedigerous segment. The division between the 
