34 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [328] 
adapted for browsing on hydroids, but yet this may not be its principal 
food, for our observations were very few on this fish, owing to its rarity; 
One of the most interesting of the hydroids, found in the rocky pools 
at low-water, or in other shaded places, is the Hybocodon prolifer, (Plate 
XXXVIIL, fig. 282.) This is one of the largest and most beautiful of 
the tubularians, and is very conspicuous on account of its deep orange- 
red color. It is by no means common, and grows only in those pools 
where the water is pure and cool, or under the shade of overhanging 
rocks. It usually grows singly or in groups of two or three clustered 
together. The delicate hydrarium of Bougainvillia superciliaris (Plate 
XXXVIH, fig. 276) is also occasionally met with in the larger tide-pools 
near low-water mark, and the small, free medusz, which are produced 
by budding from the hydrarium, are frequently found swimming in the 
waters in spring. The Clava leptostyla is a beautiful and apparently 
soft and tender species, but it grows in clusters on the fronds of Fucus 
at low-water mark, on the most exposed shores, and withstands the 
most powerful surf, unharmed. The colonies are bright light red in 
color and consist of numerous hydroids arising from creeping stolon- 
like tubes, which interlace to form the base of the colony. Each of 
the hydroids consists of a cylindrical stem, slender at base and about 
a quarter of an inch high, at the end of which there is a thicker, club- 
shaped or fusiform “head,” covered with about fifteen to thirty, long, 
slender tentacles, but the form both of the heads and tentacles is con- 
stantly changing, owing to their contractions. The small medusa-buds 
are grouped in clusters below the tentacles and do not become free. 
This species is also to be found in the pools and on the under sides of 
large stones close to low-water mark. 
The Hydractinia polyclina is often met with covering the dead shells 
inhabited by the hermit-crabs, whether in the pools or in deeper water 
off shore, with a soft, velvet-like, reddish coating, which is made up of 
hundreds of hydroids united together by their bases into a rather firm, 
continuous layer, covered with conical points. This basal layer some- 
times not only entirely covers the shell, but extends out considerably 
beyond the borders of the aperture, so as to increase the capacity of 
the interior. This is no doubt a great gain to the crab, because he will not 
be so soon compelled to exchange his shell for a larger one. Each col- 
ony of these hydroids is either male or female ; the sexes differ in depth 
of color, the male colonies being palest. But in each colony there are 
also many sterile individuals, who have to do the eating and digesting for 
the whole community, while the sexual individuals attend to the repro- 
duction of the race. Farther north, as at Nahant, Massachusetts, this 
species often incrusts broad surfaces of the rocks in the pools, but I 
have not observed it growing in this way south of Cape Cod; yet in one 
instance we dredged it growing on a rock. 
The Halecium gracile V. is frequently found growing in profusion on 
the under side of stones, in tide-pools, and attached to oysters, dead 
