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Show 1 9 0 6 . ] OF SOUTIIELIN INDIA AND CEYLON. 6 7 7 Bergli in his ‘ System' mentions 19 species of Pleurophyllidia. Of these I think that P. marmorata Kelaart is probably LAnguella cinerea Farran, though the description is somewhat vague. P. lugubris Bergh seems to have been accidentally omitted from the list. Only two species appear to have been described since : 20. P. rosea Bergh. 21. P. stenidia Bergh. To the five species of Linguella enumerated by Bergh (I. c.) may be added:- 6. L. variolosa Bergh. 7. L. cinerea Farran. (? = Diphyllidia marmorata Kelaart.) Camarga, represented by one species, C. marginata (Oersted), from the Pacific Coast of Nicaragua, seems to have a ridge in front of the rhinophores connected with the mantle by a wide commissure *. The genus Pleurophyllidiella was proposed by me (Proc. Zool. Soc. 1903, vol. i. p. 250) for a species, P. horatii, from East Africa, which appears to have no traces of branchiae or a branchial cleit, though lateral lamellae are present. The head parts appear to be as in Linguella. Bergh (Siboga, 1905, p. 208) suggests that the branchiae may be so deeply retracted as to be invisible. I doubt if this is the case. If the branchiae are merely obscured and not really absent, the more probable explanation is that they are so far from the body that they are undistinguishable from the lateral lamellae, which is much the same as saying that they have disappeared if the conformation described exists in the living animal. While fully admitting that the preserving fluid may strangely distort external features, I see no particular reason to suspect this specimen +. In several Pleurophyllidias (especially P. pallida, P. compta, and P. stenidia) the lateral lamellae are greatly reduced : in Pleuroleura both branchiae and lateral lamellae are entirely absent. The radula of Pleuroleura is narrower than in the other genera, and in one species (P. picteti) there are only four laterals. The head parts seem to be as in Linguella, though the plates show some discrepancy in this respect, probably due to distortion in preserved specimens. Some of the species are quite small, and none seems to exceed about 3 centimetres in length. Probably the total absence of a specialised breathing-apparatus is unfavourable to the growth of large molluscs. It is hard to say whether the genus should be * T am not sure that I clearly understand Bergh's diagnosis of this genus, and the figures in his Monograph on the Phyllidiadse (pi. ix.) do not throw much light on the external characters. The diagnosis is :- " Corpus minus elongatum. Clypeus tentacularis latus, semilunaris, angulis productis; caruncula nuchalis humilis, lata, in pallium commissura latiore transiens ; rhinophoria sejuncta. Sacci cnidogeni nulli." t In my description, p. 252, 1. c., the statement that the first lateral tooth bears denticles " only on the internal side " is a misprint: read " external side." |