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Show 562 REV. T. R. R. STEBBING ON CRUSTACEANS [May 22, middle of the back. But neither does Guerin-Meneville take any notice of the peculiar arrangement of the fore part of the pleon in his account of 0. emarginata, and even Pfeffer's accurate description is very ill supported by the accompanying dorsal figure of that species. It remains to consider the C. neo-zealanica Thomson, which agrees in its dimensions with C. tgpa, and is perhaps not particularly unlike in colouring-two characters, of which the second has but little importance, and the first, apart from other considerations, no importance at all. While quoting at length from Milne-Edwards's generic account of Cassidina, Mr. Thomson unfortunately does not call attention to any characters on which he relies for separating his own species from the typical one; and his specific description would, I think, justify an identification of one with the other, except for one peculiarity in C. neo-zealanica, namely, that the outer margin of the inner lobe of the uropods and the obtuse apex of the caudal shield are thickly ciliated. But the figure shows a pleon consisting of two broad, completely separated, segments, followed by the pleo-telson or caudal shield. By a comparison with the description, it appears as if the first of these segments had been regarded as the seventh of the peraeon, the first peraeon-segment being taken as a portion of the head, which is partially embedded in it. But the second pleon-segment is figured as quite simple, so that, if the figure is to be trusted, it is doubtful whether this species can stand in the genus Cassidina. The same doubt, for a similar reason, will apply to C. maculata Studer. But considering that the authors themselves have not attached any special importance to the characters discussed, there is still at least a possibility that, instead of needing new genera, all the named species of Cassidina may be one and the same. In that case, the ciliated apices in C. neo-zealanica would probably prove to be due to an adventitious growth. It would be very obliging on the part of the authors referred to, or any available representative, if they would re-examine their specimens and publish a decisive account of the required details. CASSIDINA EMARGINATA Guerin-Meneville. 1843. Cassidina emarginata, Guerin-Meneville, Icon. Regno Animal, Crust., texte, p. 31. 1853. Cassidina latistglis, Dana, U.S. Expl. Exp. vol. xiii., Crust. p. 784, pi. 52. figs. 12 a-e. 1871. Cassidina emarginata, Cunningham, Tr. Linn. Soc. Lond. vol. xxvii. p. 499, pi. 59. tig. 4. 1879. Cassidina emarginata, Miers, Phil. Trans, vol clxviii p. 204. 1884. Cassidina emarginata, Studer, Isopoden Beise ' Gazelle' p. 19. 1887. Cassidina emarc/inata, Pfeffer, Krebse von Sud-Georo-ien pp. 63-69, pi. 2. figs. 9-10, pi. 5. figs. 23-30, pi. 6. figs. 1-10. |