598 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Dorsal lamina broad, its border minutely denticulate in the pos- 
terior part of the body but nearly even anteriorly. 
Minute plication or fluting of branchial sac moderately well devel- 
oped. Seen from the inner side the ridges, which are usually at dis- 
tances equal approximately to twice that separating the internal 
longitudinal vessels, are narrower than the intervening hollows. The 
transverse vessels take part in the plication to a considerable extent 
and are of two orders, three vessels of the second (smaller order) 
generally intervening between those of the first order. Internal 
longitudinal vessels, where they cross the transverse vessels, bearing 
rather stout, somewhat curved papillae, which bend in a dorsal direc- 
tion and bear a narrow membrane along the dorsal side which is con- 
tinuous with a narrow membrane borne on the transverse vessel. 
No papillae on the internal longitudinal vessels at intermediate points 
as in the next species, and these vessels are, moreover, often inter- 
rupted about midway between the transverse vessels (see fig. 128). 
About four or five stigmata generally intervene between the internal 
longitudinal vessels but sometimes as few as three. A specimen 
47 mm. long had between 60 and 70 internal longitudinal vessels on 
one side of the sac, and about 90 transverse vessels. 
Alimentary tract smaller and less bent than in the next species. 
Stomach with internal ridges but smooth externally. Margin of anus 
irregular. 
Ovary forming a broad irregular more or less branched mass lying 
chiefly between the stomach and proximal part of the intestine and the 
branchial sac. It also encroaches a little upon the side of the stomach 
which lies against the mantle. The oviduct accompanies the rec- 
tum and ends near the anus. The male reproductive organ consists 
of numerous small rounded lobed or pyriform glands connected by 
branching ducts, and ramifies over the ovary and over a greater or 
less extent of the stomach, especially near the pyloric end. 
Although living chiefly in comparatively deep water, so that it is 
less frequently found by the ordinary collector than the next species 
(P. pnmvm), this species is both widely distributed and very common. 
In the Old World it occurs in the Siberian Arctic Ocean, on the Murman 
coast, in the White Sea, about Spitzbergen, Norway; Great Britain, 
etc., and even on a part of the French coast (Roscoff). 
In American waters it occurs in Davis Straits, on the coasts of 
Greenland and Labrador, in the Gulf of Saint Lawrence, and south- 
