590 PEOF. W. A. HEBDMAN S EEVISED 



Branchial sac with its posterior part recurved upon itself. 



Nerve- ganglion and neural gland distant from tlie dorsal 

 tubercle. 



Dorsal lamina extending behind the oesophageal aperture. 



Benal concretions always enclosed in the intestinal wall, and 

 never extending into the mantle. 



Tbis contains the single well-known species P. mammillaia^ 

 Cuv. (N.W. Eur., Med.). 



AsciDiELLA, Boule, 1884. 



Bocly attached by posterior end or left side, not incrusted 

 with sand. Branchial and atrial apertures not far distant. 



Branchial sac with no intermediate papillae on the internal 

 longitudinal bars ; not folded on itself posteriorly. Transverse 

 vessels of two sizes, placed alternately. 



Nerve-ganglion and subneural gland placed close behind the 

 dorsal tubercle. 



Dorsal lamina not continued posterior to the oesophageal 

 aperture. 



Benal concretions extending into the left side of the mantle 

 as well as the intestinal wall. 



The known species of Ascidiella* may be separated as follows : — ■ 



f Branchial sac with papillae 1 



\ No papilla; in branchial sac 2 



iWith a very wide open intestinal loop. 

 A. archaia, Sluit. (Mai.) 

 With the usual narrow intestinal loop. 

 A. venosa, O.F.M. (N.W.Eur., Med.) 

 r Fixed by a posteriorly placed peduncle. 

 2 \ A. lutaria, Eoule. (Med.) 



[ Not fixed by a posterior peduncle , 3 



{Body triangular, wide posteriorly, narrow anteriorly. 

 A. triangularis, Herdm. (N.W. Eur.) 

 Body nearly cylindrical or ellipsoidal 4 



(Dorsal lamina with a plain edge. 

 A. virginea t, O. F. M. (N.W. E., Med.) 

 Dorsal lamina with the edge toothed or irregular 6 



* Some of the older species of Ascidia which have not been re-investigated 

 lately may belong to this genus. I place here provisionally the remarkable 

 Ascidia archuia described lately by Sluiter from the Malay Archipelago. The 

 position of the ganglion is not known. " PhaUtisia scabroides," named by Ed. 

 Van Beneden and Julin, but not yet sufficiently described, appears to belong to 

 this genus. 



t The Ascidia sordida of Alder & Hancock. 



