404 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
tion in members of this family of ascidians, and the writer is not in- 
clined to attribute great weight to this difference in view of the otherwise 
close correspondence between the European and American forms. 
The European form is recorded from the west coast of Norway, 60 to 
200 fathoms (Huitfeldt-Kaas) , and Spitzbergen, SO meters (Hartmeyer), 
and from Nova Zembla, the Murman coast, and the White Sea (Redi- 
korzew, 1907a). 
Aplidium despccium Herdman (1886) collected by the Challenger 
Expedition at Le Have Bank off Xova Scotia, .51 fathoms, is probably 
identical with A. pallidum. 
Genus Amarouciu.m Milne-Edwards, 1S41. 
This genus is not sufficiently distinguished from Aplidium, from 
which it differs chiefly in usually having the colony distinctly pedun- 
culated or composed of several or many heads, and in the larger size 
of its zooids, these having the atrial orifice near the anterior end of the 
thorax and always provided with a languet, and the post-abdomen, 
when fully developed, exceeding (sometimes very greatlv) the re- 
mainder of the body in length. 
Amaroucium pellucidum (Leidy). 
PI. .35, fig. .3; PI. 37, fig. 6. 
This species exists in two very dissimilar forms, which have been 
considered distinct species (the typical A. pellucidum, and A. cun- 
stellahan Verrill), but which are in reality not even true subspecies, 
as is shown by some colonies which in one part have the typical pellu- 
cidum characters, while in the remainder of the colony the constellafum 
characters are equally well developed. There are also specimens in 
which the whole colony has characters intermediate between the two. 
The second form of this species (the A. con^tellahon of Verrill) will be 
designated in this paper A. pellucidum form constellafum, and will be 
described separately (see p. 406). The synonymy, description, and 
statements here immediately following apply to the typical form only. 
185.5. Alcijonidium ? pellucid im Leidy, Join-n. Acad. Nat. Sci. Pliiladelphia, 
ser. 2, vol. 3, p. 142, pi. 10. fig. 24. 
1871. Amouroucium pellucidNm \'errill, Amer. .Journ. Sci., ser. 3, vol. 1. p. 290. 
1871. Amouroucium pellucidum Verrill, Amer. Journ. Sci., ser. 3, vol. 2, p. 359. 
