allied to Rhabdopleura. 343 
tip of a tentacle of Coryne or the spine of an Hchinoderm. 
The ventral surface and sides of the stem are rendered plu- 
mose by a large number of long slender filaments having 
slightly bulbous extremities, and with a linear streak from base 
to tip, apparently from a groove, though traces of a septum 
also occur. These pinne apparently do not taper, and for the 
most part, in section, are composed of granular hypoderm 
with a few brownish pigment-cells. It is probably the latter 
which give in some a light pinkish or pale violet blush to the 
feathery plumes, which in life must have been finely tinted ; 
and it is further interesting that the same pigment occurs in 
Ethabdopleura. 
The arrangement of these numerous tentacular plumes wholly 
differs from that in Lhabdopleura, in which they form two 
symmetrical tentacular arms from which the pinne spring. 
Both the latter and the new form widely diverge from the 
ordinary Polyzoa in this respect, both having very mobile 
pinne that curve gracefully in all directions, instead of the 
somewhat stiffish corona and straight tentacles of the other 
Polyzoa. In Cephalodiscus they are probably of great tactile 
service; but there is little evidence from their minute anatomy 
in support of their branchial function, at least of the ordinary 
kind. ‘They thus present a much more elementary structure 
than in Phoronis. ‘They do not appear to be of much value 
as exciters of food-currents, as Prof. Lankester suggests in the 
case of Rhabdopleura; at least they could only produce cur- 
rents in the cavities of the ccencecium without special reference 
to the mouth. Both Rhabdopleura and Cephalodiscus difter 
from the ordinary Polyzoa in the absence of the tentacular web 
at the base. Both have very long pinne ; but the new form ex- 
cels Rhabdopleura in this respect. Cephalodiscus also diverges 
in regard to the thin postoral lamella, which, instead of being 
a simple triangular peak on each side, as in Lhabdopleura, 
forms a free apron-like process. Moreover it is not simply 
continuous with the tentacular arms as in Rhabdopleura, but 
the broad lamella seems rather to arise at each side, at the 
point of insertion of the basal tissue of the plumose arms, and 
it is boldly curved outward therefrom. The oral region thus 
has a different environment from that in Rhabdopleura, though 
the plan of structure is not very divergent. The distinct cir- 
cular aperture of the mouth lies in the middle line at the an- 
terior margin of the foregoing lamella, and is thus concealed 
between the opposed surfaces of the latter and the disk; and 
if these are ciliated, their influence on the conveyance of food 
into the aperture must be considerable. The oral lamella in 
some preparations passes straight up to the sides of the mouth 
