554 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
are long. If followed ventrally they are generally seen to become 
stouter and separate rows of stigmata after a little distance. Internal 
longitudinal vessels very numerous and closely placed, especially in 
the anterior and middle parts of the sac. On the interspaces they are 
generally separated by two or four stigmata; on the folds they are 
closely crowded. Their number in the anterior part of the sac of a 
rather large specimen was: 
Leftside 8 (40) 8 (40) 9 (27) 11 (22) 5 
mdt. en. 
Right side 8 (36) 10 (36) 11 (28) 13 (18) 6 
Small stunted, though fully adult indi\iduals have a considerably 
smaller total number of vessels, though they are as closely placed as 
in the larger ones. 
Stomach rather elongated, tapering in the pyloric portion, yet 
distinctly marked off from the intestine, which forms a rather large 
loop. Stomach wall with about twenty regular longitudinal plica- 
tions. Rectum long and sinuous; margin of the anus more or less 
distinctly lobed. 
Gonads two on each side. The tubular, sinuously curved ovaries 
are placed obliquely with their closed ends diverging and the open 
ends (contracted to a narrow neck with a terminal orifice with ser- 
rated margin) near together and directed toward the atrial siphon. 
The testes of each gonad consist of a cluster of pyriform or slightly 
lobed glands of different sizes attached to the mantle about the closed 
end of the ovary. Their ducts apparently unite to a common sperm 
duct accompanying the ovary and ending on a rather large papilla 
having an orifice with a serrated margin, which is situated on the side 
jof the neck of the ovary. 
Aside from inhabiting deeper water than Tethyum jxirtitum (Stimp- 
son), this species is readily distinguished by its rougher, thicker, and 
more wrinkled test, larger size, less prominent and less regularly 
shaped dorsal tubercle and by the gonads. The testes form moder- 
ately compact groups about the blind (ventral) end of the ovaries 
instead of being arranged along the greater part of the sides of the 
latter. The individual testes are, moreover, of simpler form than in 
T. partitum; the branched forms common in the latter species rarely 
if ever occur. 
This species scarcely belongs to the Xew England fauna, all the 
