BARNACLES 255 
incrusted with barnacles, and holds the ear near, the closing of 
the many doors may be distinctly heard. 
The development of Balanus from the larval stage, as also 
the anatomy of the adult, is similar to that of Lepas. When 
covered with water and unmolested, there may be seen over a bed 
of barnacles thousands of tiny fringed feet waving to and fro. 
The motions look like gestures; they are perfectly regular and 
rapid, numbering eighty to a hundred a minute. The shell 
covering formed by barnacles on piles of wharves and bridges is 
said to be a protective agent; otherwise the barnacles seem to 
have no economic value in nature, as, unlike other animals, they 
do not serve, except in very small measure, as food to other 
classes. The tautog and perhaps some other fishes feed partly 
upon them. They are sometimes an obstacle to oyster-culture, as 
they fasten upon the objects intended for oyster embryos, and, 
growing faster than the latter, soon crowd them off. One species, 
Coronula diadema, fastens to the skin of whales. It attains the 
size of two inches in diameter. The shell is half an inch thick 
and full of cavities, into which the skin of the whale is drawn, 
giving the barnacle a secure hold. (Plate LIX.) 
B. balanoides (Stimp.), B. ovularis (Gould), the rock-barnacle. 
This is perhaps the most conspicuous of the barnacles. It inhabits the 
whole northern Atlantic coast, and is so abundant that it not only 
whitens the rocks with a complete incrustation of shells, but the 
animals are so crowded that many of them lose their normal shapes and 
become greatly elongated. When the rocks are covered with water 
they seem alive, on account of the thousands of waving tentacles. This 
species also incrusts woodwork between tide-marks. 
The shell is small, white, and variable in shape; sometimes its height 
is less than the diameter of its base; again the height is several times 
greater and the summit broader than the base. In its early stages the 
valves are smooth, but later the base is scalloped by four or five grooves. 
The summit of the plates is even and blunt. The aperture is diamond- 
shaped. Two valves of the operculum are pointed at the tips; two 
are blunt, making a deep notch. in the summit. These valves are the 
distinctive feature by which to recognize this species, which varies so 
much in outward form; the species is also distinguished by its mem- 
branous base, which does not form a solid plate like that of other 
species. 
PS. eburneus, the ivory barnacle. This species, like B. balanoides, is a 
very common barnacle, and is found on all kinds of submerged wood- 
work, whether fixed or floating. It is also found on the carapace of 
