SOME ASOIDIANS FROM THE ISLE OF WIGHT. 129 



number of stigmata in the meshes, the shape of the stomach, and 

 especially the structure of the dorsal lamina. Some of these 

 differences are trivial, and it is impossible at present to say whether 

 Traustedt's single specimen of A. pusilla is, or is not, merely an ab- 

 normal individual of our species ; but the constancy in the structure 

 of the dorsal lamina in my specimens is, when associated with the 

 other peculiarities, a strong piece of evidence in favour of the 

 specific distinctness of the two types. 



Ascidia depressa is also allied to Ascidia marioni, Roule, on account 

 of the close agreement between the two species in the following 

 points — the mode of fixation, the position of the apertures, the 

 minute tuberculation of the surface, the absence of intermediate 

 papillge, the strong pectination of the dorsal lamina, the elongation 

 and approximation of the stigmata ; but the two species are of 

 course quite distinct owing to the important difference between them 

 in the structure of the subneural gland and its accessory organs. 



I have already pointed out the curious resemblance between 

 Ascidia depressa and Heller's Ascidia rudis in the histological and 

 superficial structure of the test. Since Heller's specimen agrees with 

 E-oule's Ascidia marioni both in the position of the cloacal aperture 

 and in the minute tuberculation of the surface, it is not improbable 

 that the two are specifically identical ; but whether Heller's indi- 

 vidual was rightly referred to Alder's species or not is very doubtful. 

 Alder's rudis possessed " small, distant tubercles " on the test, and 

 was " sometimes nearly smooth,^' — a condition very different from 

 that in Heller's specimen, as well as in Roule^s A. marioni. 



If, as I believe it will now be generally admitted, the forms des- 

 cribed by Heller, Roule, and Herdman under the name Ascidia 

 depressa can no longer lay claim to that title, it will be necessarj to 

 refer to them under new designations. I would propose for 

 the Mediterranean species described by Roule the name Ascidia 

 Roulei. To the variety petricola of this species. Heller's specimen 

 almost certainly belongs. I believe that Ascidia Roulei is closely 

 related to, if not identical with Alder's Ascidia rudis : but it is 

 impossible to give a final decision upon this question until our 

 British Ascidians have been collected and re-examined in greater 

 detail."^ 



The form described by Herdman as Ascidia depressa, in the 

 paper to which reference has been made above, appears to be dis- 

 tinct from Ascidia Roulei, although, it is impossible, from the want 

 of correspondence between the descriptions, to speak decisively. 

 But Prof. Herdman has himself thrown doubt upon their identity 



* It is needless to say that we look forward with interest towards Prof. Herdman'g 

 promised re-description of some of Alder ^ud Hancock's types. 



