352 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
ones in rapid succession, so that in two or three weeks the small colonies 
will increase from a quarter of an inch in breadth up to three or four 
inches, if they be situated on a flat surface, and have room to spread. 
If upon a stem or leaf of the eel-grass they will extend entirely around 
it, and perhaps several inches along its length, if not opposed by other 
colonies. At the same time the crusts increase very much in thickness. 
Thus by the end of the summer, the eel-grass, algae, stems of hydroids, 
&c., often become completely covered up by the luxuriant growth of 
this curious compound animal. The colors of this species are ex- 
tremely variable and often very elegant, and it is seldom that two 
colonies can be found with precisely the same pattern of color. 
Growing upon the same leaf of eel-grass, many diflferent colonies 
may often be found, each showing a different arrangement of the 
colors." 
Professor Verrill then goes on to describe the principal color varieties, 
to seven of which he assigns names: vars. hicolor, farinacca, annulata, 
atro.v, variegata, ulhida, and stcUa. In nearly all these forms the zooids 
are dark colored, usually deep purple or purplish brown. This color 
also ]>ervades the bulbs of the test vessels and suffuses to a greater or 
less degree the test substance during life, but when the animal dies the 
test becomes light colored and more transparent. During life, in 
addition to this dark pigment, the zooids, especially their anterior ends 
and dorsal portions, and the bulbs of the test vessels, are marked with 
a light colored pigment, which mostly disappears after death. To 
the varied shades and distribution of this pigment much of the variation 
in the color of different colonies is due. 
The zooids are of moderate size (the individual figured measuring 
about 1.75 mm. long). They lie in the colony either on their ventral 
surface with the anterior end somewhat turned up, or in an inclined 
position, as shown in the figure. The systems in which they are 
arranged contain from five to about twenty individuals, rarely more, 
and are circular or oval in outline, and usually well separated from 
each other. The posterior ends of the zooids are close together, and 
extend more or less under the common cloacal chambers which form 
the centers of the systems. 
The branchial aperture is without lobation, or nearly so. The 
atrial cavity is quite capacious and opens into the common cloacal 
cavity by the large dorsally situated atrial opening, the up]:)er lip of 
which is produced into a more or less prominent languet. The tenta- 
