588 
BULLETIN OF THE BUREAU OF FISHERIES 
Specimens about 12 mm long . — The differences between fish 10 and 12 mm long 
are not pronounced. However, the body in the larger fish is considerably more 
robust, especially anteriorly, the depth as in the smaller specimens being contained 
3.4 to 4.0 times in the length without the caudal fin. The bony ridge over and in 
advance of the eye is quite as prominent as in the smaller fish. The forehead re- 
mains very steep to vertical and projects slightly beyond the low, almost horizontal 
mouth. The gape of the mouth is now wholly below the level of the lower margin 
of the mouth as in the adult. The preopercular spines have continued to increase 
in proportionate length, the one situated at the lower posterior angle having become 
much larger than the other, being equal to the length of the eye in one specimen, 
but somewhat shorter in others. It is probable that the preopercular spines, which 
are not present in the adult, reach their greatest development at this stage and that 
they gradually decrease in size in larger fish. Specimens of the proper sizes for a 
study of the recession of these spines, however, are not at hand. A small fleshy 
tentacle is now visible over the eye for the first time. Although nearly or quite as 
long as the eye in the adult it is scarcely as long as the pupil in fish 12 mm long. A 
definite notch between the spinous and soft portions of the dorsal fin is present, as 
in the adult. No pronounced development in pigmentation has taken place since a 
length of 10 mm was attained. However, dark areas and spots about the head 
have increased somewhat in size and number in at least some specimens. A row of 
very small black dots still persists on the base of the anal. The dots are not evenly 
spaced and not definitely on each interradial membrane, although some variation in 
this respect exists (fig. 89). 
Figure 89 .—Hypsoblennius hentz. From a young fish 12 mm long. 
Unfortunately no specimens ranging from about 13 to 24 mm in length are at 
hand, and therefore, a complete picture of the development of the late juvenile stages 
cannot be given at this time. Specimens 25 mm long are “young adults” and have 
virtually all the characters of mature fish. In such specimens the prominent bony 
ridge over each eye, very characteristic of the young, has disappeared entirely; the 
fleshy tentacle over the eye is nearly or quite as long as the orbit, the preopercular 
spines no longer are evident; the caudal fin is round; and pigmentation is complete and 
similar to that of fully matured fish. Although the series is not complete, the largest 
young (12 mm long) at hand have developed sufficient adult characters to make 
identification certain. The extremely steep forehead in the young and the size, shape, 
and position of the mouth are quite characteristic of the adults and unlike the other 
local species of blennies. Furthermore, the fins are rather fully developed and the 
shape and number of their rays agree with those of the adult. 
