?.uo.s on the Natural Group of Tunicata. 533 



The Tethya of Aristotle, or, as Pliny calls them, the Tethea, 

 are in general incapable of locomotion ; and the three species 

 of which I now propose to explain the structure, seem all to 

 have been dredged from the bottom of the Northern seas, where 

 they lay fixed either to submarine rocks, sand, or sea-weed, or 

 to other animals sedentary like themselves. These species all 

 belong to the natural family of Ascidida, which corresponds in 

 every respect but name with M. Savigny's Tethyes simples. 



Subgenus. BOLTENIA Sav. 



External Character. Body with a coriaceous test, sup- 

 ported from the summit by a long pedicle, and having 

 both orifices lateral and cleft into four rays. 



Anatomical Character. Branchial pouch dLiy'iAed into lon- 

 gitudinal folds, surmounted by a circle of compound 

 tentacula, and having the reticulation of its respiratory 

 tissue simple. Abdomen lateral. Ovary multiple. 



This generic character differs in some respects from that of 

 M. Savigny, and is reformed, for anatomical reasons, which I 

 shall hereafter explain at length in my description of the only 

 species of the subgenus which I have seen from the late Expedi- 

 tion. It is the same species of Linnean Ascidia concerning which 

 Captain Sabine says in the Appendix to Captain Parry's First 

 Voyage, that it was not unfrequently taken by the trawl on the west 

 coast of Davis's Strait, in lat. 70". It is also, as this ardent lover 



shows the affinity of these to Pyrosoma, and of Pyrosoma to Salpa or (as it is some- 

 times called, although the name is preoccupied in Botany) Thalia. De Blainville, in- 

 deed, goes so far as to call the Liicida " Salpiens aggreges"; and although no great 

 stress ought to be laid on this author's arrangement, from his obvious wish to obliterate 

 the inimitable labours of Savigny, it is clear that the aflBnity between Pyrosoma and 

 Salpa is strong. A fifth group of the Tunicata is wanting to connect the Bipliorida 

 with the Ascidida; and I have no doubt that such animals will soon occur to reward 

 the industry of those who collect Mollusca and Acrita. 



3 z 2 of 



. Un\ 



