VAN NAME: SIMPLE ASCIDIANS. 447 
ized genus of ascidians. The peculiarities of the branchial sac and 
their development from the simpler type characteristic of Eugyra 
are described at length in the systematic part of this paper. One 
species of Tethyum [Styela], T. mortensetii Hartmeyer, is unusual in 
the degree of reduction of the folds of the branchial sac, but aside 
from this, the only form whose peculiarities call for special mention 
here is a small species of the family Caesiridae [Molgulidae], Caesira 
singularis sp. nov., in which the gonads are of a peculiar form, the 
folds of the branchial sac are reduced to an unusual degree, and the 
tentacles are unbranched. The last mentioned character is unique 
in that family, as far as the writer is aware. 
The family best represented is the Caesiridae [Molgulidae] with 
13 species, 12 of them in the genus Caesira [Molgula], which is thus by 
far the best represented genus in the region. The Pyuridae [Cynthi- 
idae or Halocynthiidae] are few, but the Tethyidae [Styelidae] are 
well represented, having 11 species in the region, of which 7 are 
included in the typical genus Tethyum [Styela]. The extensive genus 
Pandocia [Polycarpa] of the same family has, however, but one repre- 
sentative, and the important family Phallusiidae [Ascidiidae] but two 
or three. Omitting doubtful forms and varieties, but adding the 15 
species of compound ascidians described by the writer in a previous 
paper, there are 49 species of ascidians recorded from the region. 
Pelagic Tunicata (Pyrosomidae, Salpidae, etc.) are not included in 
the scope of either of these papers, and the writer will not attempt an 
estimate of the number of species represented. 
The writer has taken advantage of this opportunity to describe 
also three deep-sea forms found off the Atlantic coast of the United 
States as well as one which is not known to range as far north as New 
England. 
The list of new species from New England and eastern Canada 
described in this paper is as follows : 
Caesira lutulenla. 
" robusla. , 
" intumescens. 
" singularis. 
Tethyum atlanticum. 
The following new deep-sea species are also described: 
Caesira verrilli. 
Pandocia albatrossi. 
