NTTDIBRANCHIATE MOLLUSCA FROM THE EASTEEN SEAS. 139 



or six radiating papillae on either side, deeply cleft in the middle. Dorsal tentacles 

 situated upon thickish footstalks, from which spring one large hranch (the uppermost) 

 and four shorter branches, forming altogether a radiating sheath, in the midst of which 

 is a slender laminated tentacle. Marginal processes in seven pairs, the anterior longest 

 and most compressed, the posterior pair small and rudimentary. Each pair of papilla? 

 varies in size and development : the first pair consists of three elongated bodies of the 

 size of the largest branch in the radiating sheath of the tentacles ; the second pair has 

 two such ; the third and fourth also, but smaller ; the last pair has but one. On the 

 inner side of each of these bundles is a finely ramified dendriform branchia, not so large 

 as the processes, the processes and branchia all arising from a common stem. Foot long, 

 and pointed behind. Anus situated on the right side, between the dorsal tentacles and 

 first pair of papillae. 



Colour and general appearance. — Body beautifully marbled all over with streaks of 

 vermilion, strongest on the back, and more delicate and faint on the sides of the foot. 

 Papillae tipped with vermilion, and also the radiating projections of the veil, but neither 

 are marbled like the body. Dorsal tentacle-branches also tipped with vermilion, and the 

 largest branch marbled. 



Three specimens of this beautiful species rewarded a brief search among the rocks near 

 the landing-place at Aden in March. They were under stones, not far from high-water 

 mark. The animals were extremely active, often swimming with a lateral vermicular 

 movement, at which time the body was laterally compressed. They were seldom quite 

 at rest. 



I here specifically distinguish this form, although previously * I inclined to regard it 

 as the B. digitata, Adams t ; but a more careful examination since discloses points of 

 difference which had previously escaped my notice. B. digitata was first found at Sunda 

 on floating fuci, but it has since been got on the Madras coast by Sir Walter Elliot J, and 

 in the Philippines by Professor Semper §. Bergh § enumerates six species belonging to 

 the genus, and he adds very considerably to the account of the anatomy furnished by 

 our countrymen Messrs. Alder and Hancock ||. 



DESCRIPTION OF THE PLATES. 



The line beside certain of the figures denotes the natural size of the animal. The separate figures of 

 tentacles, branchial tufts, and other parts are all considerably enlarged. 



Plate IX. 



Figs. 1-5. Doris pecten, Coll., n. sp. : 1, general view of animal, its dorsum; 2, under surface of same ; 

 3, a dorsal tentacle (rhinophore) ; 4, a branchial tuft ; 5, outline of the animal at rest. 



* " Observations on the Distribution of some Species of Nudibranchiate Mollusca in the China Sea," Ann. & Mag. 

 Nat. Hist. 1868, ser. 4, vol. i. p. 91 ; and ' A Naturalist's Rambles in the China Seas' (London, 1868), p. 9. 



t Voyage of the ' Samarang," p. 07, pi. six. fig. 1. X Trans. Zool. Soc. vol. v. p. 131. 



§ Iteisen im Archip. d. Thilipp. Band ii. Heft 7, p. 301. || Loc. cit. T. Z. S. swpra. 



SECOND SEKTES. — ZOOLOGY, VOL, II. 19 



