196 MARINE INVERTEBRATES 
sometimes thrown upon the beach by storms. It grows in erect tufts, 
sometimes a foot long, and is much branched; the branches grow 
around the stem in a spiral manner, forming dense clusters. The lower 
part of the stem is often naked (having lost the branches) and bright 
orange in color, while the tufts of branches at the top are pearly-white 
or yellowish. The cells are long, with a long, pointed spine on the upper 
outer angle. Like all species of Bugula, it has bird-head appendages, 
which can be seen under a powerful glass. (Plate L.) 
B. Murrayana. Clusters of broad, thin, flexible fronds, one to two 
inches high, attached by a slender base and spreading in entangled 
masses; fronds wedge-shaped, flat, dividing in a forking manner; outer 
cells have bristle-like filaments, which constantly beat the water; all 
cells have avicularia, or bird-head appendages. (Plate L.) | 
B. flabellata. Fan-shaped fronds of flat branches, divided in a fork- 
ing manner; the cells are arranged in four or five longitudinal LOWS, 
are oblong, with a spine at each side of the circular aperture, and 
are capped with pearl-like ovicells. This species, like others of the 
genus, bears the very singular structures known as avicularia, or bird- 
head appendages. They show, under a strong glass, a hooked beak, 
like that of the hawk or parrot. These beaks are attached by flexible 
stems and are provided internally with powerful muscles by which they 
are coustantly opened and closed; the beak can bite with considerable 
force. In this species they are attached to the sides of the cells. (Plate L.) 
Genus Flustra 
F. membranacea. This species forms gauze-like incrustations on the 
fronds of seaweeds, and is common on Fucus and Laminaria, spreading 
irregularly over several inches of space. The cells are oblong, quad- 
rangular, with a blunt, hollow spine at each angle. Many species have 
simple horny tubes, closed on top, rising from some of the cells to the 
height of half an inch. (Plate LI.) 
Genus Membranipora 
M. pilosa. An incrusting variety, composed of a single layer of cells 
spreading irregularly over the surfaces of stones, shells, and seaweeds, 
sometimes completely covering the 
fronds of Chondrus crispus, Phyllo- 
pora, Rhodymenia, and other alge. 
The cells are membranaceous, with a 
caleareous rim, and have one long 
hair and several small ones surround- 
ing the large roundish apertures. It is 
found in abundance on the shores from 
Long Island Sound to the Arctic Ocean. 
c Foe . “ineata. Cells oblong, crowded, 
OR ul closely adhererit ; slender spines on edge 
os ae of aperture, which bend over and meet 
, Membranipora pilosa; afew of the cells it: i ke d shells i 
seen from above, magnified. 2, Membrani- across 1 > Incrusts roe S ana shelis 10 
pora pilosa ; a single cell, seen in profile. broad, thin, radiating patches ; cells 
