546 SIR CHARLES ELIOT. 



the mantle over the back (ahnost like Placobrauchus) and conceal their gorgeous colours, thus 

 entirely altering their appearance. When swimming, they flap the sides of the mantle and 

 bring the two edges of the foot together so as to form a sharp keel. When in captivity 

 I have often observed them adopt an almost vertical position, standing on their heads and 

 walking, or at least feeling their way with their large tentacles. They are very voracious 

 and browse freely on sponges, sertularias, polyzoa, etc. 



Bergh has justly observed that it is very difficult to determine the species of Hexa- 

 hranchus without, or even with, an anatomical examination. Perhaps most of the so-called 

 species are merely varieties. Most of them are very imperfectly described, and even in those 

 cases where the description is adequate it is not always plain what are the specific 

 characteristics beyond colour. There are unfortunately no notes as to the colour of the 

 animals in the present collection when living. As preserved they are of an almost uniform 

 dirty yellow. The family is recorded only from the Indo-Pacific (E. Africa, India, Philippines, 

 Polynesia, Red Sea). 



The peculiar arrangement of branchiae displayed in this genus is also found in the 

 Bathydorididae and Kalinga. The former are deep-sea forms, with strong jaws and a radula 

 provided with a median tooth, and are thus allied to Doridoxa and Tritonia. The buccal 

 parts of Hexabranchus, though unusually powerful, show a near approach to the ordinary 

 type of the cryptobranchiate Dorids. The affinities of Kalinga are very uncertain. Bergh 

 places it among the Polyceradae. 



Gen. Hexabranchus^ Ehr. 



3. Hexabranchus faustus B. 



I somewhat doubtfully refer to this species a specimen from the S.W. reef of Hulule, 

 Maldives. It is 14 cm. long, and considerably broader across the gills (7'3) than across the 

 head (5-4). The mantle is crinkled at the sides, but quite straight and simple in front. 

 It is compressed against the sides of the body, but the free edge when pulled out and 

 extended measures 2'5 cm. The rhinophore sheaths are slightly raised and quite smooth. 

 The groups of branchiae are set rather close together, and are not always distinct. They 

 appear to be usually 8, but might perhaps be divided differently. Each group consists of 

 several, generally 4, tripinnate tufts ^ The anal papilla is central, wide, but not very promi- 

 nent. Near it are the renal pore and the other orifice alluded to. The labial armature 

 and radula are both strong and dark brown, the former consisting of two furrowed plates 

 composed of a compact mass of small and slightly bent rods. The latter contains about 

 45 rows of simply hamate teeth, there being about 70 teeth on each side of the rhachis in 

 every row. The tentacles are large, foliaceous, furrowed down the middle, and with crinkled 

 edges. Reproductive organs as usual. 



4. Hexabranchus digitatus n. sp. 



One individual from Hulule S. reef, 7'8 cm. long and .5'2 broad, the breadth being 

 much the same in front and behind. The specimen is very much retracted and corrugated 



' Bergh in S. R. Hefte xiii., xvi. and Supp. i. aud iu Exploring Expedition, vol. xn. (Gould). 

 Ergebnisse einer Reise nacli d. Pacific, Schauinsland, Opistho- - Prof. Bergh gives the number of branchiae as 6, but the 



branchien, 1896-7. Several species are described iu the plate shows 7. 

 voyages of the Bouite, Astrolabe, and the United States 



