140 WALTER GARSTANG, M.A. 



is very different in the two cases. Prof. Herdman in the same paper 

 noticed the existence of tubercles on the dorsal lamina of Ascidia 

 plebeia, so that there is no reason to suppose that he overlooked them 

 in his A. depressa. 



Lastly, M. Koule has described under the name Ascidia depressa, a 

 species which, while probably identical with Heller's, is undoubtedly 

 distinct from Alder's species, The mode of attachment, the shape of 

 the body, and the structure of the branchial sac are very different in 

 the two cases. The species described by Heller and by Roule presents 

 a close affinity with Ascidia mentuia, and still more, perhaps, with 

 Alder's (not Heller's) Ascidia rudis ; but there is nothing in Alder's 

 description of A. depressa to indicate a similar relationship for that 

 species, and my specimens are distinctly against it. 



Ascidia depressa, as now re-described, is very closely related to 

 Traustedt's Ascidia (Phallusia) pusilla (Mitt. Zool. Stat. Neap., iv, 

 1883, p. 465, Taf. xxxiv, figs. 16, 17 ; Taf. xxxv, fig. 26). The chief 

 points of difference are found in the different proportions of the length 

 to the breadth of the body, the length of the siphons, the breadth of 

 the largest horizontal vessels of the pharynx, the 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 abnormal 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 papillae, the 

 strong pectination of the dorsal lamina, the elongationand 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 Roule's 



