TWO RARE BRITISH NUDIBRANCIIS. 161 



Our knowledge of the internal anatomy of these forms is limited to 

 the preliminary paper by Prof. Trinchese before referred to. The 

 cutting-edge of the jaw is short and armed with a single series of 

 15-16 teeth, the first two or three of which are simple, the rest set 

 with extremely fine tubercles. Radula triseriate ; the teeth of the 

 median row with lateral denticles ; the lateral teeth broad, unarmed 

 ("quasi omnino illi Galvinarum similis," Bergh*). Salivary glands 

 large. Liver diffuse, with anterior and posterior branches, the latter 

 supplying the dorsal papillae. The nervous system similar to that of 

 iEolidiidse. Eyes well developed. Otocysts with a single otolith. 

 Penis unarmed. The spermatozoa similar to those of iEolidiidse. 

 Hancockia appears to be mature when about half an inch in length. 

 Trinchese describes ripe generative products at this stage, and Gosse 

 has figured and described the spawn deposited by a specimen of this 

 size. The ribbon was in the form of two complete figure-of-eight 

 coils, the ova being irregularly scattered. My specimen was only a 

 quarter of an inch long, and during the fortnight that I kept it no 

 spawn was shed. 



I stimulated Hancockia to see if the dorsal papillae would respond, 

 as they do in Lomanotus ; no effect, however, followed. The presence 

 of cnidocysts in the genus described by Trinchese as occurring at the 

 tips of the pleuropodial lobes (loc. cit. pp. 186, 189, and plate, figs. 8 

 and 14) makes its behaviour contrast still more with that of Lomanotus. 



While gliding over the bottom of the vessel in which it lived it 

 would sometimes stop, raise the anterior part of the body, and, with 

 the velar tentacles and the rhinopores well expanded, it would sway 

 from side to side. In a short time the action ceased and the animal 

 went straight to the Delesseria on which it lived. Unfortunately I 

 made no experiments to ascertain whether Hancockia responds to 

 shadows as stimuli. The large eyes noted by Trinchese would be in 

 favour of such reaction. Hermosa bifida, which lives on Delesseria, 

 and certain Eolids have been shown by Mr. Garstang to respond, t 



As regards the systematic position of Hancockia. Gosse placed it 

 in the Tritoniidse ; Trinchese, Bergh, Norman |, and Cams place it 



* " Die Cladohepatischen Nudibranchien," Zool. Jahrb. v. p. 53. 



t Garstang, " Complete List of Plymouth. Opisthobranchs," Jour. Mar. 

 Biol. Assoc, (n. s.) i. no. 4, p. 423. 



t " Revision of British Mollusca," Ann. & Mag. N. H. vol. vi. 1890, p. 79. 



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