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Show 642 SIR C. ELIOT ON NUDIBRANCHS [June 19, identical, for, though the variations may be within specific limits, it is equally possible that two dissimilar forms, both varying, may roughly coincide. For the determination of species the most important internal characters are the radula and labial armature, the other organs not varying much in the genus. Good external characters are often furnished by the greater or less development of the dorsal margin, which in several species bears small knobs underneath. In a few species the back bears tubercles or even papillae (Chr. papulosa B., Chr.? roseopicta Verrill). The precise number 6f branchiae is not a character of importance, but the species seem divisible into those where the plumes are few (3-7), moderately numerous (8-12), and many (12-20 or more). In some species the plumes have a strong tendency to develop accessory branches and become bipinnate. Chromodoris ( ? )amabilis (Kelaart). (Plate XLII. fig. 1.) (Kelaart, 1. c. I. pp. 294-5.) This form is perhaps a Chromodoris, though the bipinnate branchiae create some doubt. It may even be Chr. porcata (Bergh in Semper's Reisen, xvi. 2, pp. 831-3), which is white or yellowish with purple spots on the back, yellow rhinophores, white foot and branchiae. The gills are 8 and two of them subdivided. It is recorded from Mauritius. Chromodoris fidelis (Kelaart). (Plate XLII. fig. 2.) (Kelaart, 1. c. I. p. 295. Bergh, System, p. 1106. Cf. Bergh, Chr.flammidata & Chr. lacteavsi Siboga-Expeditie: Opisthobranchia, pp. 151 & 159-160.) This form, which is said to be common at Trincomalee, will probably be recognised by its striking coloration. It is possibly identical with Chr. flammidata B., which has black gills and rhinophores, and is said to be red with a broad irregular white patch down the centre of the back. This is merely another way of regarding a pattern which Kelaart describes as a white surface, " the edge lined with red and irregular tooth-like transverse internal prolongations of the same colour." In other details, such as shape, number of branchiae, and the anterior expansion of the foot, the two forms agree. Chr. lactea B. appears to be a closely allied form. It is pure white with black branchiae and rhinophores, and differs chiefly in not having the red border. The radula is much the same as that of Chr. flammidata, but there are some differences in the labial armature. Chromodoris treciosa (Kelaart). (Plate XLII. fig. 3.) (Kelaart, 1. c. II. p. 295. Bergh, System, p. 1106.) This form appears to belong to the group of Chromodorids which are somewhat flat and have an ample mantle overhanging the foot all round. ° |