432 PROF. W. A. HEEDMAN ON BRITISH TUNICATA. 



while A. onentula has about five), while the tentacles are small 

 and distant, 25 to 30 in number, and larger and smaller alter- 

 nately. The A. truncata of Part I. may be a large, rough, and 

 somewhat deformed variety of A. aspersa, 0. F. Miiller, perhaps 

 the form described by Alder as A. pustulosa ; my A. triangularis, 

 on the other hand, is probably a small neat form of the same 

 species {A. aspersa), corresponding to that described as A. aculeaia 

 by Alder. If one compares A. truncata and A. triangularis^ one 

 with another, it seems almost absurd to regard them as one 

 species ; but viewed in the light of Alder's A. pustulosa and 

 A. aculeata, and of various intermediate varieties I have found 

 since, I have very little doubt that they are the extreme forms of a 

 series which must be regarded as belonging to Ascidiella aspersa, 

 0. F. Miiller. 



My A. Pato7ii may, I think, be referred to A. venosa. It 

 agrees well with the species which Alder and Hancock called 

 venosa, and which is usually called venosa now, in general ap- 

 pearance and in the simple condition of the branchial sac, which 

 is quite exceptional amongst species of Ascidiain-not being longi- 

 tudinally plicated. I feel, however, somewhat doubtful whether 

 this is really the A. venosa of the ' Zoologia Danica.' 0. F. 

 MUller's figure f and description show the atrial aperture as 

 more than halfway down the body, while in the British speci- 

 mens I have seen it is near the anterior end. The test also seems 

 more flaccid and gelatinous in the northern form. 



Finally, A. exigua of the former paper is probably the young 

 of some other species, perhaps of A. pleheia ; but I am not sure, 

 as it appears to differ a little from all species known to me. I 

 ought not to have described so small, and, as I now think, 

 immature looking, a form as the type of a new species. 



In regard to the other species referred to in Part I., I have 

 nothing to alter; and I still hold to the relationships of the 

 species and genera given there, except that I have since adopted 

 the genus Ascidiella of Eoule (1884) for those forms in which 

 the nerve-ganglion and subneural gland are placed close to the 

 dorsal tubercle. This genus includes the following British species : 

 A. venosa, A. virginea, A. aspersa, and A. scahra, which can be 

 readily distinguished as follows : — 



* See Part I., Linn. Joui-n. Zool. vol. xt. p. 280 et seq., pis. xv. & x\i. 

 t Zool. Dan. tab. xxv. 



