ASCIDIA PLAXA. 97 



In the same region small caeca have been observed, but 

 they are very inconspicuous. 



This species is evidently closely related to A. Alderi. 

 The loop of the intestine, as in it, is placed crosswise, 

 and the viscera are attached to the test by a mem- 

 branous process which passes into the intestinal loop, 

 just as a similar process does in that species. A.plana, 

 liOAvever, is sufficiently distinguished by the number 

 and arrangement of the tentacular filaments, the form 

 of the branchial papillae, and the character of the vas- 

 cular ramifications of the test. 



We have seen only two individuals of this species, 

 and they had both been some time in spirit before 

 they were examined; so with respect to colour little is 

 known. But in consequence of the blood-corpuscles, 

 which are very numerous, remaining of a dark brown 

 colour, this is one of the best, if not the very best, 

 species for the determination of the vascular system. 

 The blood-channels can be traced on almost any part 

 of the organism, even to their minutest ramifications. 



9. Ascidia Alderi Hancock. 



(PI. XVII, fig. 7; PL XIX, fig. 6; and figs. 7 and 20 



in text.) 



[Ascidia Alderi HANCOCK in Ann. Nat, Hist. (4) VI (1870), 

 p. 356.] 



Bod if irregularly ovate or pyriform, produced 

 towards the upper end, of a yellowish horn-colour 

 inclining to flesh- tint, with a few small, scattered 

 tubercles ; attached diagonally by the base and about 

 half way up the side. Apertures produced, distant, 

 with longitudinal tuberculated ridges ; the branchial 

 aperture terminal, the anal about two thirds down 

 the body, and inclined towards the left side ; ocelli 

 red. Test moderately thick, firm, transparent, with 

 the terminal twigs of the blood-channels appearing 



7 



