MR. MACDONALD ON A NEW GENUS OF TUNICATA. 79 



51' S., long. 159° 28' E.) was a very remarkable Ascidian, which, 

 as it appears to be quite new, merits brief notice. 



The external appearance of the animal so much resembled 

 the nidamental case of some large Gasteropod, affixed to a 

 block of coral, that no suspicion of its real nature was entertained 

 until it had been minutely examined. Soon, however, it was 

 ascertained that within a thin coriaceous test, fashioned like a 

 snuff-box, with a perfectly applied lid, a little tunicary was en- 

 closed, enjoying the power of opening and closing the operculum 

 or door of its retreat at will. 



The case (figs. 1 & 2) was about ± an inch in length, and over | 

 of an inch in breadth, though rather fuller in front than behind. 

 The attached side was flat (fig. 2), but the free surface (equivalent 

 to the right side of the recumbent animal) was convex and rounded 

 {d) ; so that the aperture at the anterior end presented a D-shaped 

 or semicircular figure (fig. 4) ; and this was accurately fitted with 

 a lid of a corresponding shape. The free margin of both the aper- 

 ture and the lid was beset with minute and rigid spines, having an 

 inward curvature protecting the entrance from invasion. In con- 

 tinuity with these margins a thin layer of test-substance was 

 traceable as a kind of conjunctiva (fig. 4 c), upon the anterior 

 part of the contained animal, to the borders of tbe branchial (d) 

 and cloaca! openings (e), which occupied the same plane in the 

 mouth of the cell, being merely divided by a narrow transverse 

 depression. Both these openings were simple though somewhat 

 puckered in the contracted state, and encircled at a little distance 

 from the free edge by a broad band of pale-red pigment. 



The mantle was closely applied to the inner surface of the test, 

 without, however, giving off any palliovascular processes. A dark- 

 coloured reticulation, visible through the outer epithelium, marked 

 off the distribution of the blood-vessels ; and the disposition of the 

 internal organs was traceable through the semitransparent tissues 

 (fig. 3). 



!N"ot wishing to destroy the specimen, I did not determine the 

 arrangement of its respiratory membrane ; but I observed that 

 the branchial orifice was guarded by a circle of simple tentacula 

 (fig. 4 d). 



The oesophagus was short, soon opening into a subglobular 

 stomach with thick glandular walls thrown into longitudinal folds. 

 The intestine proceeded from the posterior end of the stomach, 

 around which it turned inferiorly, and having coursed forwards to 

 within a short distance of the cloaca! opening, it ended in the vent. 



