392 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
rays. Examples of the regular forms are shown in text-figs. IS and 19. 
Some colonies seem to lack altogether not onl_y regular spicules, but 
calcareous deposits; at least the writer found none in the portions 
examined microscopically. On the other hand, some colonies have 
the regular spicules so numerous that the specimen acquires something 
of the opac{ue white appearance of a Didemnum [Leptoclinum]. In 
such colonies the surface 
often shows a small sharp- 
ly defined area of each 
zooid in Avhich the spicules 
are less abundant and the 
test consequently less white 
and opaque. 
The zooids measure, 
when expanded, about 2 
mm. in length, the com- 
paratively long neck be- 
tween the thorax and ab- 
domen, and the many 
divisions of the testis giv- 
ing them a superficial re- 
semblance to those of the family Polycitoridae. The muscles of the 
mantle, including the sphincters of the aj)ertures, are very weak and 
inconspicuous. 
In some colonies, at least, a large majority of the fully developed 
zooids have two long club-shaped vascular processes extending out 
into the common test from the region of the esophagus. In some cases 
one of them forks or divides into two branches. Apj^arently their 
wall consists of a single layer of cells, which are flattened, except at the 
expanded end of the process, where they become high and columnar. 
Perhaps more carefully preserved material might show a more com- 
plex structure. The processes contain a few corpuscles. Inside the 
body the processes are continued as two narrow thin-walled tubes, 
which run up (anteriorly) along the esophagus close against its wall. 
They become gradually smaller and appear to end without communi- 
cating with the esophagus or branchial sac. 
The branchial aperture is six-lobed; the atrial aperture is large, 
thin-bordered and without lobes, but with a short languet, which 
extends but little beyond the margin of the aperture. The tentacles 
Text -fig. 19 
ules. X 515. 
■ LissocUniwi aiireum Verrill. Spic- 
