422 
BULLETIN OF THE BUREAU OF FISHERIES 
most of the spines (anterior ones) developed. They are very slender and become 
short and usually indistinct, or are missing, posteriorly, and generally no definite 
count can, as yet, be made. The heterocercal character of the tail has disappeared 
completely. The membrane between the vent and the origin of the anal, pre- 
viously described, has become narrower, and the almost vacant space is gradually 
becoming smaller. The pigmentation remains essentially the same as described for 
7.0 millimeter specimens, except that the black peritoneum no longer is visible 
through the body wall 
and a few dark mark- 
ings are present on the 
base of the caudal. 
(Fig. 46.) 
Specimens 20.0 
millimeters long . — The 
body at this age (size) 
Figure 46 . — Leiostomus xanthurus. From a specimen 15 millimeters long , • , i 
continues to be more 
slender than in the adult, the greatest depth being contained in the length to base 
of caudal about 3.8 times (adults about 2.6). The dorsal outline is quite convex 
but not nearly as much so as in the adult. All the fins, including the spinous dorsal 
are well developed, and it is possible to enumerate for the first time all the dorsal 
spines. The posterior margin of the caudal fin at this size is distinctly concave. 
The fish is still without color, except for the few pigment spots described for smaller 
individuals. At this age, as well as in much younger individuals, there are distinct 
spines on the preopercular bones, which disappear later. (Fig. 47.) 
Specimens 25.0 millimeters long . — No pronounced changes in the development 
occur between a length of 20 and 25 millimeters. The body has become propor- 
tionately deeper, and 
the back is higher. 
The mouth is less 
oblique and somewhat 
more inferior. A va- 
cant area between the 
vent and the origin of 
the anal, previously 
occupied only by a 
semitransparent 
. . Figure 47 . — Leiostomus xanthurus. From a specimen 20 millimeters long 
membrane, is now 
filled in with heavier tissues, leaving only a slight concavity. The principal develop- 
ment between a length of 20 and 25 millimeters is that of pigmentation. A dark 
chromatophore previously situated on the side, a little in advance of the origin of the 
anal, has disappeared. The rest of the dark spots, extending along the ventral edge 
from the origin of the anal to the caudal are still present, as in much smaller indi- 
viduals. A row of vertically elongate dark spots on the base of the caudal fin has 
become more pronounced, and new chromatophores have appeared about the mouth, 
on the head, and a row of widely spaced ones along the upper edge of the back. A 
very small chromatophore is present on the median line of the side of the caudal 
peduncle, slightly in advance of base of caudal, and a few dark points of even smaller 
size lie in the same plane forward of it. A dark spot situated about at the “hinge” 
