MOLLUSCA OF PLYMOUTH. 409 



41 of liis paper represents the teeth of an Aplasia taken in Vigo 

 Bay, having " forty rows of divergent teeth ; the median broad, pro- 

 duced at the base, reflexed, tricuspid ; centre cusp prolonged and ser- 

 rated." This Aplysia received no specific name in print, but Mr. 

 Hogg has added in his own copy the word punctata, an identification 

 which there is every reason to believe to be correct, although the 

 shape of the posterior margin of the basilar portion of the tooth is 

 unusual. Mr. Gwyn Jeffreys, however, confused matters by taking 

 this radula for that of an A. depilans, and that of Mr. Hogg's A. 

 hyhrida (Fig. 42) as the normal one of A. punctata. Mr. Hunt 

 follows Gwyn Jefi'reys' identification, but suggests that " 70 " is 

 an accidental misprint (1. c, 1877, p. 401), or that the numbers 40 

 and 70 should be transposed. The latter of these suggestions is 

 impossible, because the central tooth of the radula of an Aplysia 

 depilans numbering seventy rows is not so distinctly tricuspid, nor 

 is the centre cusp prolonged and serrated. It is best, I think, to 

 leave this confusion unsolved, and to hope that the radulse of Aplysia, 

 as well as the other structures, may be investigated and described 

 again for the different species at different stages of growth. 



Shell. — The shell of our Plymouth Aplysia punctata is figured on 

 PI. XXYIII (figs. 8 and 9) for two individuals of different ages, the 

 larger shell (represented of the natural size) being taken from the 

 individual numbered " 10 " in the table of measurements. This 

 shell is considerably larger than that figured by Vayssiere for 

 A. punctata, and is intermediate in character between that shell and 

 the shell of A. depilans, just as Vayssiere's shell is intermediate in 

 character between those shown in my figs. 8 and 9. Canon Norman 

 has kindly forwarded to me a shell of A. depilans from Palermo, 

 which I have represented by fig. 10. It is much broader than that 

 of the same species figured by Vayssiere, and its left edge is much 

 more curved, the margin of the anal excavation also sloping con- 

 tinuously forwards (in the natural position), and not forming a true 

 " bay " like that of Vayssiere's. As Dr. Norman has stated (Rev. 

 Brit. Moll., 1. c, p. 60), Mr. Hunt's large shells closely correspond 

 with those of Mediterranean A. depilans. I have been favoured 

 with three of the shells of the Torbay A. depilans, and the two 

 largest agree in character with the shell sent rae by Dr. Norman, 

 the curvature of the left side being a little less convex ; but the 

 smallest of the three, measuring 1^ inches long by 1 inch wide, has 

 its anal margin sloping away much more and is less flattened than 

 the larger ones. It approaches the shell of A. punctata in this 

 respect. Indeed, when the shell of the young A. depilans is de- 

 scribed I doubt if it will be dibtingui-shable from that of A. punctata, 

 even if it is not the same. 



