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Show 644 SIR C. ELIOT ON NUDIBRANCHS [June 19, identical gorgeous coloration. But there are differences of detail in the buccal parts, and the branchiae of Chr. sykesi have not been observed to be subdivided like those of Chr. inopinata or to be so long. Casella. This genus, though offering hardly any structural differences from Chromodoris, is easily recognisable by its undulated dorsal margin, which is generally marked by a conspicuous border. Casella rubra Bergh, 1905, seems to be a distinct species, but it may be doubted whether the other specific names cover more than one species which appears in several colour varieties. Casella maccarthyi (Kelaart). Doris maccarthyi Kelaart. Chromodoris maccarthyi (Kelaart). Casella cincta Bergh. ? Casella atromarginata (Cuv.). (Kelaart, 1. c. I. p. 292. Bergh in Semper's Reisen, xi. pp. 462-3 ; xvi. 2, pp. 831-37 ; xvii. pp. 941-4.) Two drawings are preserved and also a specimen from Ceylon. The drawings represent a pinkish-grey Casella with the characteristic strongly undulated margin. There are no spots or mottlings of any kind, but the mantle is bordered with bright blue, the upper part of the rhinophores is blue, and there are indications of blue on the stems of the branchiae. The preserved specimen corresponds with the drawing. The colour is of a uniform greyish yellow without a trace of spots. The mantle-edge is marked by a purplish-brown border, with traces of an accompanying white border particularly on the under side. The length is about 28 mm. and the maximum breadth nearly 20 mm. The mantle-margin is strongly undulated, but narrow, particularly behind. The rhinophore-sheaths are distinctly raised, but the margins of the branchial pocket are not elevated. The branchiae are retracted. The buccal mass has been removed. There can be but little doubt that this is the Casella cincta of Bergh. It has all the characters, except that the back is not spotted and the foot is not bordered with blue. The branchiae are given as fewer (15 as against 22), but the difference is not important, and it is very likely that the smaller branchiae were not visible outside the pocket. The preserved specimen was not opened in order to preserve the appearance. I think that Casella cincta and Casella atromarginata are merely varieties of one species which shade into one another through various shades of blue, purple, and black. If this is so, the species must be called C. atromarginata (Cuv.) and the blue-bordered form var. maccarthyi. If thought advisable, the term var. cincta can be used for forms with a blue border and a spotted back. |
