558 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
in the area immediately around the openings purphsh with minute 
radiating streaks of flake-white; the four large lobes are brownish, 
with numerous small specks and streaks of flake-white, which often 
predominate over the ground color." 
Test very variable in thickness, but thicker near the siphons; 
tough and leathery, smooth internally, rough and more or less fibrous 
externally. Length of largest specimens 25 mm. to 30 mm. 
iVIantle rather thin but strong, not adherent to the test in preserved 
specimens. Musculature light, the superficial layer an almost con- 
tinuous sheet of fibers, the deeper muscles gathered into imperfect 
bands which radiate from the bases of the siphons. 
Tentacles rather numerous (forty to fifty in large siDecimens) of 
several sizes arranged with a variable degree of regularity. 
Dorsal tubercle very variable in form, but usually of a modified 
U-shape (often with one horn much incurved), the open interval point- 
ing anteriorly or more or less to the left. 
Dorsal lamina plain and rather narrow. 
Branchial sac with four folds which are narrow in comparison to the 
intervening spaces. The first fold is highest, the fourth lowest of all. 
Transverse vessels numerous and slender, of at least four orders, 
arranged with some regularity. Those of the third order merely cross 
the stigmata in the dorsal part of the sac (those of the fourth order 
are wanting there) but become stout and separate the stigmata in the 
ventral region, and fourth-order vessels appear in the intervals there. 
Internal longitudinal vessels slender and not very numerous, generally 
separated by from eight (in the ventral region) to five or six (in the 
dorsal region) stigmata on the interspaces, but quite close together 
on the upper part of the folds. A medium-sized individual of average 
characters had them distributed thus on the right side: 
mdi\ 5 (18) 4 (13) 4 (14) 5 (9) 2 en. 
On the left side the first fold began nearer the median dorsal vessel 
and but two vessels intervened instead of five. 
Stomach somewhat elongated, with 18 to 30 longitudinal folds in 
the wall. Intestinal loop moderately large. Margin of anus with a 
variable number (often about a dozen) rounded lobes, but in some 
individuals the lobes are not greatly developed, the margin being 
merely sinuous and more or less plicated. 
Gonads two on each side. Each comprises an elongated sinuously 
