Lepeophtheirus dissimulatus — Lewis 
235 
length of the inner. The exopodite and the en- 
dopodite differ from those of the preceding stage 
in shape and armature. The one-segmented ex- 
opodite is broader than long, the lateral margins 
are irregular although slightly convex, and the 
distal margin is irregularly rounded. Both the 
outer and inner lateral margins have several 
irregularly spaced setules and the distal surface 
bears two spinelike processes. The one-seg- 
mented endopodite is about one-half the length 
of the exopodite although both the length and 
width of the segment are approximately equal; 
the lateral margins are almost parallel, the distal 
margin slightly rounded, and the inner distal 
surface gives rise to two spinelike processes. 
The third thoracic leg of the third chalimus 
(Fig. 20c) is distinctly different from that of 
the second chalimus. It appears that the third 
chalimus marks a distinct change in the first 
three pairs of thoracic legs. The protopodite is 
now broader although the added breadth ap- 
pears to have been gained as a result of a length- 
ening of the distal margin or an inclusion of 
the inner lateral margin with the distal; both 
the exopodite and the endopodite are now two- 
segmented and the armature has changed. 
The protopodite of the third thoracic leg of 
the third chalimus is broad and flattened. The 
greatest width, across the proximal end, is 
slightly less than twice the length; the inner 
lateral margin appears to be incorporated into 
the distal margin although distinct evidence of 
this is lacking. A single plumose seta is present 
just lateral to the junction of the protopodite 
and sternal plate. The exopodite, attached to 
the lateral region of the distal protopodite sur- 
face, is two-segmented, the first segment slightly 
shorter than the second; the outer margin of 
the first segment is convex, the distal margin 
sloping to the proximal margin in older speci- 
mens but not distinctly so in younger specimens. 
The second segment is as wide as long, the lat- 
eral margins are irregular, the distal margin is 
rounded, and the surface bears three lightly plu- 
mose setae. The endopodite is two-segmented 
although the division between the first segment 
and the protopodite is indistinct in older speci- 
mens. The outer margin of the first segment is 
longer than the inner, and the proximal and 
distal margins are irregular. The second segment 
is approximately equal to the greatest length of 
the first segment and is almost circular in out- 
line. 
The protopodite of the third thoracic leg of 
the fourth chalimus (Fig. 20 d) is broader than 
that of the third and the length has also in- 
creased so that the greatest proximal width is 
only about three-fourths of the greatest length. 
TABLE 4 
Armature of Third Thoracic Legs of Developmental Stages* 
STERNAL 
EXOPODITE 
ENDOPODITE 
STAGE 
MARGIN 
PLATE 
PROTOPODITE 
1 
2 
3 
1 
2 
Chalimus I 
outer 
2p' 
2h 
inner 
2h 
Chalimus II 
outer 
c,2h 
inner 
c 
2h 
Chalimus III 
outer 
IP 
3P 
2P 
inner 
lP,f 
IP 
IP 
Chalimus IV 
outer 
IP 
3P 
lp,2P 
inner 
lP,f 
IP 
IP 
Chalimus V 
outer 
f 
f,lP 
c,4p' 
c 
c,2P 
inner 
lP,f 
1 lp,lH' 
5P 
IP 
2P 
Chalimus VI 
outer 
f 
f,lP 
c,lp' 
c,3p',lP 
c 
c,lp,3P 
inner 
lP,f,2s 
1H' 
IP 
3P 
IP 
2P 
Adult 
outer 
f 
f,lP 
C,lp' 
c,3pMP 
c 
c 
inner 
lP,f,2s 
1H' 
C,1P 
c,3P 
IP 
c,5P 
For explanation of symbols see Fig. 1. 
