152 THE VOYAGE OF H.M.S. CHALLENGER. 



The Do7'sal Tubercle is in the form of a transversely flattened band crossing the 

 anterior end of a deep triangular peritul)ercular area. 



The Alimentary Canal is placed on the left side of the body in its posterior half 

 Tlie oesophagus is long, the stomach small, and the intestine relatively short. The 

 oesophagus is anterior to the intestine, and the whole canal forms a loop open dorsally. 



Tlie Reproductive Organs form a globular mass placed on the dorsal edge of the 

 stomach and filling up the loop between the cesophagus and the intestine. 



Xom%.— March 3, 1874; Station 157; lat. 53° 55' 0" S., long. 108° 35' 0" E ; 

 depth, 1950 fathoms; bottom, Diatom ooze; surf. temp. 37°"2, bottom temp. 32°*1. 



This is an important species which appears to be more nearly allied to Ahyssascidia 

 than to any other genus of the Ascidiidce ; and although it does not conform with all the 

 characters of that genus as given in the first part of this Eeport (p. 193), I have con- 

 sidered it better to place it here in the meantime, than to form a new genus intermediate 

 between Ahyssascidia and Ascidia for its reception. 



In external appearance (PL XL fig. 1) it is like an Ascidia. It has an eight-lobed 

 branchial and a six-lobed atrial aperture, and the latter is placed upon a posteriorly 

 directed siphon like that of Ascidia plebeia, Alder. The vessels in the test are very 

 numerous, and form a conspicuous feature (PI. XL fig. 1) as they are distinctly seen 

 through the transparent test. 



The body inside the test is greatly contracted, so as to appear only about three- 

 quarters of the size necessary to fill its cavity (PI. XL fig. 2). The short wide branchial 

 siphon and the long narrow atrial are readily seen. The viscera are placed upon the 

 left side of the body, and the mantle on that side has no muscle liands. The long 

 tentacles are seen projecting freely out of the branchial aperture (PI. XL fig. 2). 



The branchial sac has a very loose and fragile appearance, the reason being that all the 

 vessels are very narrow and the spaces between them large. The internal longitudinal 

 bars are especially thin, but bear very large papillae (PI. XL fig. 4), and are united to the 

 transverse vessels by large membranous flaps. The general appearance of this branchial 

 sac recalls that oi Ahyssascidia ivyvillii. 



'- The dorsal lamina is evidently formed of a series of languets (PI. XL fig. 5) which 

 have been united by a membrane. In Ahyssascidia ivyvillii^ there are short languets. 

 The closely placed tentacles (PI. XL fig. 3) are remarkable for their great length, 

 stretching easily for half their extent outside the branchial aperture. The smaller 

 tentacles are exceedingly narrow. The conditions of the dorsal tubercle and peri- 

 tubercular area are seen in PI. XL fig. 3. Probably the dorsal tubercle in Ahyssascidia 

 ivyvillii is in much the same condition. The nerve ganglion is long and narrow. 



The oesophagus commences about half-way down the dorsal edge of the branchial 

 1 See tliis Report, Part I. p. 19J. pi xxvii. fig. 11. 



