[ 367 J 



XXVIII. Oil the Anatomical Characters of three Australian species of Tunicata referable 

 to Savigm/s subgenus Caesira. By John Denis Macdonaxd, F.Jl.S., Assistant Sur- 

 geon of II. M.S. ' Herald,' commanded by Captain H. M. Deniiam, B.N., F.E.S. 

 Communicated by George Busk, Esq., F.B.S., F.L.S. 



Read January 20th, 1859. 



I. 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 Amjihibolis, covered with a similar granular coating, and so fai* 

 exhibiting a corresponding habit. As this little tunicary forms the type of a well-marked 

 genus, of wliich we have discovered several species, a short description of it may not 

 be uninteresting. 



The body is of a depressed pyi-iform shape, and from one-half to three- foiu-ths of an 

 inch in length. It generally rests a little on one side, as weU 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- 

 tiu-e, however, is obscurely divisible into six rays instead of foui". 



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. 



The pallio-vascular 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. 



On remoATng the test, an elaborate system of reticulated vascular canals, invested with 

 a greenish-yeUow pigment, presents itself beneath the epithelium of the mantle and the 

 more superficial fibres of the muscular coat. 



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 Boltenia ; and, as in the latter 

 genus, the inner rim of the same opening is surrounded by compound tentacula, divided 

 into pretty equal l)ranchlets and pinna?. 



The branchial network is composed of rather stout transverse bars and very delicate 

 longitudinal nervurcs, strengthened at intervals by stronger ones assuming the character 

 of folds. 



The mouth is situated at that part of the respiratory chamber which is nearest to the 

 cloacal cavity, and leads by a very short esophagus almost directly into an elongated 



