138 BRITISH 1TXICATA. 



The alimentary tube is wide, and fills the lower two- 

 thirds of the pallial sac ; it is closely folded upon itself, 

 and the rectal portion rises up perpendicularly to the 

 atrium; the anal margin is smooth, narrow, and 

 reflected. The vesicular matter coating the tube is 

 inconspicuous, the nuclei, however, give to much of 

 the surface a minute freckling; the vesicles themselves 

 are quite small. 



The ovary is composed of branched radiating tubes 

 spread over the right side of the upper portion of the 

 intestinal loop. A few of the extremities of the 

 branches pass round the margin of the loop and 

 appear at the left side. The male caeca are seen at 

 both sides of this portion of the digestive tube, but 

 are most conspicuous on the right side ; they are 

 small, clustered, and somewhat lobecl. 



At first sight Axe! did offini* has considerable re- 

 semblance to A. xurdidii, and the mode of aggregation 

 into groups is very similar in both species; the colour, 

 however, is different, and the deficiency of branchial 

 papillae in the former shows that its alliance is with 

 A. scabra and its associates. And of these it seems 

 most nearly related to A. JYortnani ; it is distinguished, 

 however, from that species not only by its colour, and 

 comparative absence of echinations, which are almost 

 entirely confined to the tubes, but by numerous other 

 points of detail, amongst which may be mentioned the 

 form of the left oral appendages, and the great thick- 

 ness of the free margin of the papillary membranes. 



26. Ascidia pustulosa Alder. 

 (PI. XVI, figs. 1-3 ; PI. XVIII, fig. 10.) 



Ascidia pustulosa ALDER in Ann. Xat. Hist. (3) XI [1863], 

 p. 154. 



Sod// ovate, rugose, horn-coloured, adhering towards 

 the base. Apertures sessile, strongly tuberculated or 

 echinated, reddish, the branchial terminal, the anal 



