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Show 6 5 6 SIR C. ELIOT ON NUDIBRANCHS [June 19, surmised by Bergh, is identical with Th. maculigera. Unfortunately the buccal parts have been taken out of both the Newcastle specimens, and we must be content with Alder and Hancock's statement:-" Tongue as in D. tuberculatci: no collar." This, of course, ought to mean that all the teeth are simply hamate and smooth, whereas in Bergh's Th. maculigera and in my specimen from Zanzibar the outermost teeth bear hairlike denticles. It is probable that there is some variation in this respect, for the shape of the teeth is not exactly similar in my specimen and in Bergh's. Also, after examining Alder and Hancock's two specimens, I am inclined to think that the animal described by me (I. c. p. 368) as Th. stellata is merely a variety of this species. It differs from the typical form in its harder consistency, stellate branchial pocket, and in that the outermost teeth of the radula are entire. The outermost teeth are found to vary within the limits of the same species in Platydoris argo and Haigerda formosa, being sometimes smooth and sometimes denticulate. T ho rd isa crosslandi Eliot. (Eliot, Proc. Zool. Soc. 1903, ii. p. 368. Cf. Bergh on Diaulula ? gigantea in Siboga-Expeditie, Opisthobranchia, 1905, p. 119.) After re-examining my specimens, I think this species is identical with the Diaulula gigantea of Bergh. The two descriptions are in general agreement and there are some remarkable coincidences in details. In both the nervous system is much concentrated ; there is a large prostate, and the penis has a curiously twisted shape, somewhat as in Phialodoris. The dimensions and coloration also agree. There are two points of difference, which perhaps admit of explanation. Firstly, in Th. wosslandi there is a minute, but quite distinct, labial armature. I have found it in all the specimens which I have examined, but it may easily escape notice and may possibly really disappear in some individuals. Bergh found 70 rows of teeth in the radula, and " in den Reihen schienen 150-200 Platten vorzukommen." If this means 150-200 teeth on each side of the rhachis, the radulae in my specimens were smaller and do not exceed 50x110.0.110 as a maximum. Secondly, Bergh describes the dorsal surface as " iiberall fein und dicht granulirt, die Ncippchen gerundet, hier und da auch Kegelformig." An inspection of my specimens, confirmed by notes in the living animal (v. Eliot, I. c.), shows that the back is covered with elongate pointed papillae, sometimes bearing filaments at their tips. But when preserved in alcohol they often become round owing to contraction and accidental pressure, and sometimes disappear entirely, although in life they are 2-3 mm. long. The distinction between the genera Diaulula and Thordisa is perhaps not very clear. Bergh's diagnosis of the former is " Notaeum holosericeum [explained as " sammetartig "]. Dentes |