VAN NAME: SIMPLE ASCIDIANS. 513 
65 mm. long and 54 mm. in height and equally large ones from West 
Spitzbergen, Greenland, and the northern North Pacific. Wagner 
records much larger specimens (90 mm. long) from the White Sea. 
In the Bay of Fundy region the individuals do not usually exceed 
30 mm. or 40 mm. in length, but occasional larger ones occur. 
Mantle musculature well developed, siphons very muscular. Strong 
bands radiating from the siphons extend for a distance on the sides 
of the body. A rather close network of slender muscle bands crossing 
each other in various directions (though transverse bands predominate) 
covers most of the body. 
Oral tentacles of four or five orders, the larger ones very complex 
in their branching, being three or four times compound, and notable 
for the great number of small simple or nearly simple, often rudimen- 
tary and nodule-like branchlets which are borne on the trunk and 
larger branches as well as on the smaller ones. These branchlets end 
in blunt, rounded, often slightly swollen tips. In a number of speci- 
mens examined there were usually five very large (but not all equally 
large), complex, branched tentacles alternating with a like number of 
considerably smaller ones, and between these several other orders 
of smaller and less complex ones arranged more or less conformablv 
to the usual scheme (1, 4, 3, 4, 2, 4, 3, 4, 1, etc.). Very small simple 
or slightly branched tentacles were also present in the intervals, but 
not in large numbers, at least in the specimens studied. 
Dorsal tubercle large, C-shaped with the open interval toward 
the right and the horns spirally incurved. 
Dorsal lamina plain-edged. 
Branchial sac with seven well developed folds on each side. It is 
difficult to say whether the internal longitudinal vessels should be 
regarded as confijied to these folds or whether the two vessels at the 
base of each fold should be reckoned as belonging to the interspaces 
dorsal and ventral to it, since they usually lie a little removed from 
the fold, though clearly belonging to the group borne on the fold. 
The largest folds bear (including their outlying ones) about twelve 
vessels. 
Transverse vessels of sac of four or five orders, seven of them of the 
first order. As these diverge from each other in the ventral parts of 
the sac, a few of the vessels of the next smaller or second order become 
stouter and assume the role of vessels of the first order in that part of 
the sac. The smaller transverse vessels are in general well developed 
