420 
BULLETIN OF THE BUREAU OF FISHERIES 
prominent swelling (hump) over the eyes and another at the nape. The hind gut is 
prominent and appears to be entirely free from the body distally. (In larger speci- 
mens it is plainly connected by membrane, and the membrane may have been broken 
in these larvae.) A fin fold is present but rays are not yet evident in any of the fins. 
The dark membrane (peritoneum) lying dorsally of the abdominal cavity is plainly 
visible through the thin wall and is 
crescent shaped (conforming to the 
contour of the dorsal wall) when the 
fish is viewed from the side. An 
elongated dark chromatophore lies 
Figure 41 —Leiostomus xanthurus. From a specimen 1.7 millimeters dorsally of the hind-gut. In addi- 
long tion, a row of dark chromatophores 
is present along the ventral edge of the entire caudal portion of the body. 
Specimens 3.6 millimeters long. — The principal development that has taken place 
between this size and the smaller ones (2.8 millimeters) already described, is the 
appearance of rudiments of rays on the ventral side of the distal part of the tail. 
The fin developing here is destined to become the caudal fin. The mouth at this 
age (size) is less strongly oblique than in the younger individuals, already described. 
A dark chromatophore is present 
at the hinge (joint) of the man- 
dible, situated slightly behind 
the vertical from middle of eye, 
and a few small indefinite dark 
specks are sprinkled over the 
head. (Fig. 42.) 
Specimens 4.0 millimeters 
long. — The principal develop- 
ment that has taken place, since a length of 3.6 millimeters was attained, consists of 
the greater development of the caudal fin. The notochord, usually, although not 
always, is curved upward at this size giving the tail the appearance of being hetero- 
cercal. In some specimens, as in the one drawn, the notochord remains straight, how- 
ever, the caudal rays being below it and directed obliquely downward. The dorsal pro- 
file of the head has become much more even in outline, the depressions and the humps 
having largely disappeared. 
The fin fold is prominent, 
and usually no thickening of 
the membranes in the regions 
somewhat later to be occu- 
pied by the dorsal and anal 
fins has taken place. (Fig. 43.) 
Specimens 6.0 millimeters 
long. — At this size the caudal 
portion of the body has become proportionately much deeper and the break in the 
ventral outline between the body and tail is much less pronounced than in younger 
individuals. The caudal fin is fairly well formed and its base (oblique in smaller 
fish) now is in a vertical plane, the notochord being strongly curved and ending at 
the base of the upper rays. A thickening and a slight projection of tissues has taken 
place in the region that will be occupied by the base of the anal and for a part of 
Figure 42 . — Leiostomus xanthurus. From a specimen 3.2 millimeters long 
Figure 43 . — Leiostomus xanthurus. From a specimen 4 millimeters long 
