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 rows, 

 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 constantly 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 specimens 

 have simply 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 algae. 

 The cells are membranaceous, with a 

 calcareous 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. 

 M. lineata. Cells oblong, crowded, 

 closely adherent ; slender spines on edge 

 of aperture, which bend over and meet 



l,Membraniporapilosa;&fevrotthe.ce\\e. _ jf . i nprns f s rocks and shells in 

 seen from above, magnified. 2, Membrani- f CF< V. ii 



pom pilosa; a single cell, seen iu profile. broad, thin, radiating patches J Cells 



