418 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The zooids are rather small, the example figured measuring less 
than 4 mm. without the post-abdomen, though as can be seen in the 
figure, it was expanded to an extent unusual in preserved specimens. 
The post-abdomen often exceeds the rest of the body in length. The 
muscle bands in the mantle are mostly longitudinal and are narrow 
and cjuite numerous. 
The branchial orifice is six-lobed; the atrial orifice is usually more 
conspicuously lobed than in A. glabnim and has a rather short simple 
languet. There are about a dozen tentacles in all, of two sizes placed 
alternately. The branchial sac has about 12 rows of stigmata with a 
maximmn number of about 17 or 18 in a row on each side. Near the 
endostyle the stigmata become successively shorter, but maintain their 
full length at the dorsal end of the row. The stigmata begin quite 
near the endostyle and extend to the median dorsal vessel, which is 
slenderer and inconspicuous, though the transverse vessels are muscu- 
lar. The dorsal languets are very short, stout, somewhat curved, and 
directed posteriorly. They arise from the transverse vessels of the left 
side about opposite the second stigma from the median dorsal vessel. 
The wall of the stomach has about a dozen deep and regular longi- 
tudinal folds. There appears to be nothing unusual in the structure 
of the reproductive organs. 
All the si)ecimens unquestionably of this species in the collection 
are from Vineyard Sound, Mass., and vicinity, which is also the only 
place where the writer has collected it. The most favorable situation 
for its growth is where there is a stony or gravelly bottom and a strong 
current. Such places exist at many points in Vineyard Sound and 
especially in the channel at Wood's Hole, where, in summer at least, 
the bottom is literally covered with the plate-like masses or colonies 
over large areas, and in dredging the dredge often becomes completely 
filled with them. Though it is a shallow-water species, the writer has 
never found it near low-water mark, but always in water at least a 
couple of fathoms in depth. Coues and Yarrow (1878) report its 
occurrence on the North Carolina coast as follows: 
"Very abundant on rocks and stones near Beaufort, and on the piles 
of the wharf at Fort Macon. This species attains a large size and the 
rapidity of its growth is surprising; new clean piles used to repair a 
wharf were in less than four months well covered with large clusters of 
this ascidian." The writer has not found it growing on piles on the 
New England coast, and does not feel certain that their specimens 
