ri re 
XXVIII. On the Anatomical Characters of three Australian species of Tunicata referable 
to Savigny’s subgenus Cæsira. By Jonn DENIS MACDONALD, F.R.S., Assistant Sur- 
geon of H.M.S. * Herald, commanded by Captain H.M. Dunnam, R.N, FRS. 
Communicated by GrorcE Busk, Esq., F.R.S., FLS. ER, 
Read January 20th, 1859. 
1. IN ‚another paper, on the anatomical characters of Perophora Hutchisoni, I had occa- 
sion to notice the frequent occurrence of a small sessile and solitary Ascidian, attached to 
the same branches of Amphibolis, covered with a similar granular coating, and so. far 
- exhibiting a corresponding habit. As this little tunicary forms the type of a well-marked 
genus, of which we have discovered several species, a short description of it may not 
be uninteresting. 
The body is of a depressed pyriform shape, and from one-half to three-fourths of an - 
inch in length. It generally rests a little on one side, as well as on its base, being thus 
in part sessile and in part recumbent. | 
The two external openings lie nearly on the same plane, and in general appearance, 
more especially in the contracted state, resemble those of Boltenia, a resemblance which 
is heightened by an infolding of the test extending between them. The branchial aper- 
ture, however, is obscurely divisible into six rays instead of four, — å | 
- The test is exceedingly thin, and so densely studded with fine grit, that it is rather 
difficult to investigate its structure satisfactorily ; an internal glistening coat of a fibrous 
texture is nevertheless distinctly traceable. | HE, 
The pallio-vaseular system, which is so highly developed in other cases, is scarcely at 
all visible in the present species, a circumstance most probably to be accounted for by 
the thinness of the test, the greater part of whose apparent thickness is due to extraneous 
matters. en i | : 
On removing the test, an elaborate system of reticulated vascular canals, invested with 
à greenish-yellow pigment, presents itself beneath the epithelium of the. ausnile and the 
‚More superficial fibres of the muscular coat. Piece Oe oP Sag | 
The outer part of the branchial opening is armed with a circlet of simple, pointed or 
bifid tentacula, the equivalents of which are also present in Boléenta ; and, pe the latter 
genus, the inner rim of the same opening is surrounded by compound tentacula, divided 
Into pretty equal branchlets and pinnæ. | | | 
The branchial network is composed of rather stout transverse poe 
longitndinal nervures, strengthened at intervals by stronger ones assuming the c er 
of folds. - Tu | = 
The mouth is situated at that part of the respiratory | hamber which 18 — to v = 
eloacal cavity, and leads by a very short æsophagus almost directly into an elonga 
bars and very delicate 
