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Show 360 SIR C. ELIOT ON XUDIJJUAXCHS [Dec. 1, prostate is present in both Discodoris and Platydoris, which are otherwise so distinct, and is absent in Archidoris but present in Anisodorw, which are otherwise identical, (iii.) In many genera is present an armature of the reproductive organs, that is, one or many spines, hooks, or plates generally only on the male branch. The value of this feature, as estimated by the concomitance of other important characters, varies. In the families of Dondopsidae and Phyllidiadae and in the well-marked genus Platydoris of the Cryptobranchiata an armature is, so far as we know, characteristic. On the other hand, we find two genera like Diaulula and Gargamella apparently identical but for its presence or absence. In the Aeolidiada/ also a hook or spine is present or absent in closely allied genera. It appears to m e that such an armature is not sufficient to constitute generic rank without other characters. (/) T n e other internal organs do not offer many features which serve our purpose of classification. It does not appear that we can unite the forms in which the stomach is enclosed in the liver, or in which there is only a single instead of a double blood-gland, or in which the nervous system is very concentrated. As a result of these considerations, I think that the most profitable way of classifying new Dorids of the group treated of here, is to refer them when possible to the following genera taken in a wide sense :-Archidoris, Discodoris, Thordisa, Trippa, Halgerda, Kentrodoris, Platydoris, Asteronotus, and Sclerodoris (gen. n.). N o doubt, remarkable forms have been and will be found which require special genera for their accommodation, but the majority of species seem to m e to fall under one or other of the divisions mentioned. Archidoris is distinguished by a fairly plump shape, broad foot, and a warty or tuberculate back. No member of this group is known to possess a labial armature, and a genital armature is rare. The radula generally consists of uniform, simply hamate teeth: more rarely some or all are denticulate. I include in this genus, in its wide sense at least, Anisodoris, Homoiodoris, and Artachcea. As mentioned above, though it is easy to define the generic characters of a typical Staurodoris, the genus seems to pass into ArcMcloris by a complete series of connecting links. Discodoris.-I should be inclined to extend this genus so as to mean flat, oval animals, not hard, with both foot and mantle-brim fairly broad. Back granulate. A genital armature is usually absent; a labial armature is either present (Section Discodoris) or absent (Section Peltodoris). Thordisa.-Flat, soft animals, much like Discodoris, but with the back neither granulate nor warty, but covered with soft pointed papillae. No member of this group is known to possess a well-developed labial armature, though a rudimentary one is found in Th. crosslandi, |
