VAN NAME: SIMPLE ASCIDIANS. 547 
the siphons to the attached end of the body. Superficial to these 
is a weaker layer of muscles encircling the body. 
Oral tentacles of two or three sizes, not very numerous, about 
thirty in number. 
Dorsal tubercle C-shaped, the horns incurved, and the open interval 
directed obliquely forward and to the left. 
Dorsal lamina rather wide, plain-edged, but its margin laterally 
plicated in contraction. 
Branchial sac without folds, the internal longitudinal vessels quite 
regularly placed and but seventeen on a side in this specimen, though 
perhaps they would be found more numerous in older individuals. 
But two or three stigmata, which are of short oval form, generally 
intervene between these vessels, though there are four or five in the 
spaces along the median dorsal vessel and endostyle. Transverse 
vessels of three orders regularly arranged, very numerous; those of 
the first order exceeding thirty in number. 
Alimentary tract lying mostly posterior to the branchial sac. 
Stomach elongated, with about twenty longitudinal folds; esophagus 
and intestine long, thin-walled, also with longitudinal plications. No 
pyloric caecum observed. Margin of anus with many short rounded 
lobes. 
Gonads one on each side, consisting of a central ovary of elongated 
tubular form bordered on each side with a row of small, simple pyri- 
form or, less often, two-lobed male glands. These communicate by 
short ducts with the common sperm duct which accompanies the 
ovary and ends on a papilla beside the neck into which the ovary 
narrows at the anterior end. 
This species is of wide distribution. In the Arctic seas it is nearly, 
if not completely, circumpolar, occurring in the Siberian Arctic Ocean, 
the White Sea, about Iceland, Greenland, etc., and at many points 
on the coasts of northern Europe, including Scotland and England. 
On the American Atlantic coast it has been reported by Packard 
(1867, 1891) from Labrador (Straits of Belle Isle, Salmon Bay, 15 
fathoms, sandy bottom), by Whiteaves (1901) from the Gulf of Saint 
Lawrence between Cape Breton and Prince Edward Island, and 
Northumberland Straits, and by Stimpson from Massachusetts 
(10 miles east of Boston Light). 
It occurs on sandy, less often on muddy bottoms or on those partly 
stony, but rarely on hard rocky bottoms, and ranges from 6 to 100 
fathoms. 
