446 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
be the same species was described as new by Metcalf (1900) (see p. 
464) in an important paper dealing chiefly with points on the anatomy 
and histology of various ascidians. 
The lists of ascidians given among those of other invertebrates by 
Packard (1891) and Kingsley (1901) are compilations from some of the 
above works, but Whiteaves' (1901) list of Canadian Invertebrata 
contains new matter concerning this group. The last mentioned 
writer did much collecting in Canadian waters, and some of his earlier 
papers (notably that of 1874b) also record facts about ascidians of 
that region, all of which, however, are summarized in his list of 1901. 
Recently Michaelsen (1908b, 1912) has described a new species 
(Pyura pedenicola) and a new variety (Dendrodoa kukenthali var. 
'pedenicola) from the Banks of Newfoundland, but the writer cannot 
regard them as distinct from previously described forms. 
It is not within the scope of this review to mention papers of a 
purely anatomical or embryological nature, nor those of European 
writers dealing with species common to America and European waters, 
but the work of Hartmeyer (1903) on the Arctic ascidians in Romer 
and Schaudinn's "Fauna Arctica" cannot be passed without mention, 
as it gives so much information about many species found in the New 
England region that it has taken a place of the very first importance 
in the literature of the New England ascidians. 
As in the case of the compound ascidians, the published facts con- 
cerning the simple ascidians of the Atlantic coast south of New 
England are few and scattering and the specimens at hand so few that 
it has not seemed best to attempt to cover that region in the present 
paper. 
General Notes. 
Leaving out of account all uncertain forms, 34 species of simple 
ascidians, distributed in 6 families and 12 genera, are here recorded 
from the region this paper deals with. All the more important fami- 
lies of simple ascidians are represented. The region cannot, however, 
be called unusually rich in number of species, neither are there many 
whose structural characters present any striking peculiarities. The 
most interesting of them is Traustedt's genus Bostrichobranchus. This 
is evidently derived from the genus Eugyra Alder and Hancock (1870), 
from which it differs in the multiplication of the infundibula of the 
branchial sac. It is, in the writer's opinion, the most highly special- 
