454 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The following eight are southern forms found mainly or wholly 
south of Cape Cod. As in the case of the compound ascidians of 
similar distribution, but little is yet known about the southern limits 
of their range : 
Caesira lutulenta. Caesira singularis. 
" manhattensis. Tethyum atlanticum. 
" arenata. " partitum. 
" robusta. Ciona intestinalis var. ocellata. 
The data in regard to many of the species are insufficient for satis- 
factory generalization in regard to their distribution in depth. A 
majority of the species of the northern group range in depth from a 
few fathoms, or from low-water mark, to a considerable depth, gener- 
ally 100 to 200 fathoms. Only three of them are not recorded from 
depths of 50 fathoms or more. 
With the southern group of species this is not the case. Excepting 
two which are exclusively confined to moderately deep water some 
distance off the coast, they are shallow-water forms. 
In their habits, the species may be divided into two main classes: 
those which attach themselves to some more or less solid object, 
and those which live free, buried in the sand or mud, in which they are 
often anchored by fibrous processes of the test. The first class in- 
cludes the larger proportion of the species. A rocky, shelly, or other 
hard bottom is generally most favorable for these, for the reason that 
there they are more likely to find firm objects for attachment, but 
provided such objects are present, the character of the bottom itself 
is a secondary matter. The species which habituallj^ bury themselves 
are necessarily inhabitants of sandy or muddy bottoms. It should 
be noted, however, that such species are often found lightly attached 
to some object, or to each other. 
Of this latter group the following eight may be regarded as members : 
Bostrichobranchus pilularis. Caesira singularis. 
Caesira lutulenta. Pelonaia corrugata. 
" papulosa. Tethyum molle. 
" arenata. Pandocia fibrosa. 
Also of this group are the deep-sea species Pandocia alhatrossi and 
Caesira verrilli, though these do not properly belong to the New 
England fauna. 
Caesira manhattensis is peculiar in very often growing upon eel-grass 
(Zostera). The period of growth and life of individuals which so 
