530 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
may arise directly from the surface, or each spine from a rounded 
protuberance on the surface. They may be so numerous and minute 
as to give the surface a velvety appearance or large enough to be indi- 
vidually conspicuous to the naked eye. As the animal groAvs older and 
larger they disappear more or less completely, though some probably 
always persist. The species attains a large size; body length 50 mm. 
to 80 mm. or often more; stem, often 150 mm. to 200 mm. additional. 
In alcoholic specimens the color of the body is yellowish white or 
more or less brownish; in life the body is sometimes deep red, in other 
cases yellowish, often tinged with red. In internal structure the 
American specimens correspond very accurately with the description 
given by Hartmeyer (1903). 
Mantle musculature mainly of two layers, the deep layer (deficient 
on the ventral region) formed by the bands which radiate from the 
siphons; the superficial layer of those which encircle the body and the 
bases of the siphons. Each laA^er consists of distinct rather widely 
separated bands; together they form a network with nearly square 
meshes. 
Oral tentacles rather few; about a dozen large ones, which differ 
much in size among themselves and show some tendency to alternate 
in size, and a few smaller ones in the intervals. The largest are very 
complex in their branching (irregularly five or six times pinnate); 
the ultimate branchlets have rounded somewhat swollen tips. 
Dorsal tubercle C-shaped with inrolled horns; open interval to the 
right. 
Dorsal lamina cleft into numerous narrow teeth. 
Branchial sac with nine or ten folds (the last of which is rudi- 
mentary) on each side. The first fold is the highest; the others 
diminishing in height in quite regular succession except the second, 
which is lower than its place in the series would indicate. Internal 
longitudinal vessels very numerous in large specimens. In a mod- 
erately large one they were distributed as follows: 
mdv. 3 (30) 7 (16) 6 (24) 7 (22) 6 (20) 5 (17) 5 (14) 5 (14) 3 (9) 3 (4) 1 en. 
Stigmata placed with their long diameter transverse to the length 
of the folds, as in P. echinata. They are arranged in longitudinal 
rows, separated by vessels of varying width. In general these rows 
correspond in number to the internal longitudinal vessels, one of the 
latter passing over the middle of all of the stigmata of a row, but 
