390 Prof. J. Reid on the Anatomy and 
only a very faint ash-colour, very different from the much deeper 
ash-colour in all the dried specimens of Flustra avicularis I have 
seen. 
These two polypes ought certainly to be classed as two differ- 
ent species of the same genus, and not under two different genera. 
A new genus should perhaps be instituted for their reception, as 
their general character, and more especially the possession of 
those remarkable appendices, the bird-head processes, separate 
them from <Acamarchis, Flustra and Cellularia, the genera to 
which they are most allied. 
Pedicellina echinata. This polype is found in considerable 
quantities in front of the Castle of St. Andrew and near low-water 
mark, adhering to Cellularia reptans, to Sertularie, and to the sur- 
face of stones. It is more hardy than most of the other ascidian 
polypes, and can be kept alive at home for along time. The 
number of tentacula varies from fourteen to twenty. In some spe- 
cimens the stalk is nearly smooth, in others several spinous-look- 
ing processes project from it, and in others both stalk and body are 
covered with a long, fine and sparse down. In the young animal 
the body is relatively longer and narrower, The body in the older 
animal is very decidedly compressed from before backwards and 
elongated transversely, and is considerably narrower and more 
bulgmg at the edge in which the intestine lies (fig. 8 d) than at 
. the edge next the gullet (fig. 8a). The upper part of the body 
is bounded by a slender rim to which the tentacula are attached. 
This rim slopes slightly from the narrow towards the broad end 
of the body. The tentacula at the extremity of the narrow end 
are shorter than the others, and all of them become considerably 
broader as they approach the rim. They are connected together 
at their lower third by a contractile membrane, partly composed 
of cireular fibres. The body itself is not contractile. The imner 
surface of the edges of the tentacula and the inner surface of the 
rim are provided with strong cilia, and in the older animals the 
external surface of the tentacula is frequently covered with a layer 
of pretty large granules or cells. On examining the animal under 
the microscope when placed in water containmg a quantity of 
carmine, the movements of the currents of water produced by the 
cilia can be more distinctly observed. The two rows of cilia at- 
tached to each tentaculum do not produce currents in opposite 
directions, but both strike downwards and towards the mesial 
line of the tentaculum to which they are attached, and cause a 
current down the centre of its internal surface, by which the 
particles of carmine are carried downwards to the rim. When all 
the currents carried down the tentacula arrive at the rim, they are 
rapidly conveyed along its upper edge by the action of the cilia 
with which this portion of the imner surface is so abundantly 
