AS01DIA PLEBEIA. 119 



which are not numerous, are confined to the right 

 side ; it dies out rather abruptly immediately behind 

 the mouth ; the margin is entire. The tubercle is re- 

 markably minute and forms a simple loop with the 

 convexity turned downwards, but the left extremity is 

 occasionally bent inwards. The tentacular filaments, 

 which are long, stout, and pretty equal in size, are 

 very numerous and crowded, and are arranged in a 

 single series forming a regular collar. 



The ovary is a rather delicate, dendritic organ, and 

 ramifies over both sides of the intestinal loop, but the 

 greater portion is at the left side, and though the rami- 

 fications are spreading they do not reach so far down- 

 wards as the stomach. The minute caaca of the male 

 organ appear to be confined to the right side of the 

 alimentary tube ; at least, none were observed on the 

 other side. The species is also remarkable for the 

 large size of the cells coating the stomach, as similar 

 cells do in all the members of the genus. 



This species has affinities with A. aculeata and A. 

 depressa. From the first it may be known by its more 

 elongated form and more prominent apertures, and 

 by the papillae of the test being smaller, fewer, and 

 not echinated ; from the latter by its thinner test and 

 smaller area of attachment, as well as by the absence 

 of the thickened margin or disc which divides the 

 upper from the lower surface in that species ; and 

 from both it may be distinguished by the fragments of 

 shells with which it is usually more or less covered. 



19. Ascidia sordida Alder and Hancock. 



(PL XI, fio-s. 6 and 7 ; PI. XII ; XIII ; XVIII, fig. 4 ; 

 PL XX, fig. 7 ; and fig. 2 in text.) 



Ascidia prnuum MACGILLIVRAY, Moll. Aberdeen [1843], p. 



312. 

 Ascidia rustica DALYELL Rare Anim. Scotland, II [1848], 



p. 143, pi. xxxiv, fig. 6 ; pi. xxxv (young ? ). 

 [Non Ascidia prnniim MULL, nee A. rustica MULL. ZooL 



Danica (1788).] 



