VAN NAME: SIMPLE ASCIDIANS. 
597 
next following species (P. prunum). Apertures on low conical pro- 
jections some distance apart, the branchial larger and more prominent 
with eight or seven lobes, the atrial with six lobes (nearly rounded 
in expansion according to \'errill). Test of moderate thickness on the 
ventral region, but quite thin above, the outer surface varying from 
Text-fig. 41 
PJiallusia obliqua (Alder). X 1.7. 
smooth to somewhat wrinkled, with or without some adhering material 
(mud, algae, hydroids, etc.). In general the test substance is of a 
softer and more flabby consistency than in the next species, and varies 
from transparent or translucent to nearly opaque; it is of a greenish or 
olive tint in life, becoming a dirty gray or brown in alcohol. Size 
of largest specimen studied: length 57 mm.; width (obliquely) 42 
mm. Hartmeyer mentions specimens over 70 mm. long, from Nor- 
way, Spitzbergen, etc. 
Mantle very thin on the left side but with fairly well developed 
musculature on the right side; the muscle bands, though slender, 
are numerous and cross each other in various directions. About the 
siphons they have the usual circular and radial directions. . 
Tentacles in a moderately large individual 32, of two sizes placed 
alternately. In addition, a minute third-order tentacle occurred in 
two or three of the intervals. 
Dorsal tubercle with a crescent-shaped or U-shaped aperture with 
the open interval directed forward. One horn of the U is often irregu- 
larly bent (PI. 66, fig. 131). 
