PEOr. W. A. HEEDMAK ON BEITISH TUNICaTA. 437 



to some definite conclusion in regard to several of Alder and 

 Hancock's species. Others, from tlie condition of tlie only spe- 

 cimens, cannot now be satisfactorily determined or cbaracterized. 



1. A. plana, Huk. — I have seen do specimen of this. Ei'om 

 Hancock's short description I do not see how it can be distin- 

 guished from a small A. mentula. 



2. A.Alderi, Hnk. — I would say the same in regard to this. The 

 characters Hancock relied upon to distinguish these two species 

 are liable to great individual variation. 



3. A. ruhrotincta, Hnk. ^I have seen Canon Norman's type 

 specimen of this, obtained by him between tide-marks at Gruernsey 

 in 1865. It measures 6 cm. by 3 cm., and is of elongated elliptic 

 form, with both ends about equally rounded ; the branchial aper- 

 ture is anterior, and the atrial is more than halfway down the 

 dorsal edge and does not project so much as in a typical 

 A. mentula. It had been attached to a shell by the middle of 

 the left side ; but no stress can be laid upon the mode of 

 attachment in these forms, as it is probably to a large extent 

 accidental. 



The test is cartilaginous, but flexible and not thick ; vessels 

 are readily visible. The mantle is very muscular on the right 

 side. The branchial sac is plicated. There are very large 

 papillae on the bars. The meshes are elongated transversely. 



The tentacles are numerous, slender, and of three sizes. 



The dorsal lamina is ribbed transversely. 



The dorsal tubercle is rather small, and roughly of triangular 

 shape ; the aperture is anterior, and both horns are turned in.' 



The alimentary canal occupies the posterior two thirds of the 

 left side. 



Hancock admitted that this is closely allied to A. mentula ; and 

 with the greater knowledge we now have of variation in these 

 forms, it is, I believe, impossible to separate the two. Colour 

 is of no importance ; and the other points of difference Hancock 

 mentions are too slight to rely upon. 



I have found specimens adhering to stones and seaweeds a 

 few feet below low- water of spring tides at East Loch Tai-bert, 

 Loch Pjne, which agree well with Hancock's description of 

 A. o'uhrotincfa, and which were associated with A. mentula, 

 and were evidently the same species. 



4. A. ruhicunda, Hnk. — I have examined Canon Norman's type 

 specimens from the Hebrides and from Strangford Lough. One 



