NUDIBRANCHIATA. 553 



12. C. gracillimum Semper. 



One specimen from Kolumadulu Atoll, Maldives, 33/, of a uniform dirty yellowish-brown. 

 It is easily distinguished by its very slender dimensions. The length from the head to the 

 tip of the tail is 2'7 cm., the body being somewhat bent. The tail is very long (1'6 cm.) 

 and compressed, being only 2 mm. thick. The breadth across the back is 7 mm., and the 

 height of the dorsal process also 7 mm. The mantle and frontal veil are far more distinct 

 than in the last species and the free mantle edge measures 2 mm. The apertures for the 

 rhinophores and branchiae are very small. The specimen was not dissected. 



Two small specimens about a centimetre long from N. Male Atoll, Maldives, 27 /, are 

 perhaps referable to the same species though proportionally less elongate and slender than 

 the larger indi\'idual. 



Gen. Discodoris^ B. 



The Discodorids are soft, flat animals, of an oval or oval-elongate form. The back is 

 granulated or finely tuberculate, and in the known species generally yellow or brown -with 

 darker mottlings. The mantle edge is ample but the foot fairly wide, grooved and more 

 or less notched on the upper lip in front. The tentacles are digitiform, the branchial 

 aperture round, crenulate or stellate. There is a labial armature formed of two plates (or 

 a continuous ring) composed of minute rods. The radula consists of simple hamate laterals, 

 without a central tooth. The reproductive organs are unarmed but there are large prostates. 



Discodoris is distinguished from Platydoris externally by its softer texture and internally 

 by the presence of a labial and the absence of a genital armature. Separate genera have 

 been created by Bergh for several allied forms with a labial armature but showing various 

 peculiarities in the reproductive system. 



Discodorids are recorded from the Pacific, Indian Ocean, E. Africa, Philippines, Mediter- 

 ranean, and West Indies. They are therefore in all probability cosmopolitan. Like Platydoris 

 they are frequently found under stones between tides on coral reefs. They are lethargic 

 in their movements and several species have an extraordinary power of self-mutilation. When 

 handled, or apparently when feeling uncomfortable, they slowly detach part of the mantle, 

 or even the whole mantle edge in a complete ring. The remaining part of the animal 

 seems uninjured and lives at least several days. This self-mutilation is generally explained 

 as an attempt to escape from a foe who has seized hold of the mantle, but considering 

 how slowly it is effected and that it takes place when the animal is in capti\'ity and is 

 not attacked, though perhaps suffering from the effects of bad water, it may equally well 

 be regarded as a sign of weakness, due to unfavourable physical conditions'. 



13. D. concinna (A. and H.). 



One specimen from Minikoi. Length 4-2 cm., breadth 2"2 cm., foot 1'3 cm. wide. The 

 back is minutely tuberculate, yellowish-brown in colour with blackish spots. The tips of 



1 Bergh, .S. li. Hefte xn., xvi., x^^I., Supp. Heft i., and hours after capture. This was the case wheu they were put 



Challenger Report on Nudibranehs. Alder and Hancock, in a vessel quite alone without any other animal or object 



Notes on a Coll. of Xitd. Moll, made in India, 1863. which could alarm them. The division always took place at 



* This self-mutilation is particularly frequent in a species exactly the same point, just in front of the last pair of dorsal 



of Genu common at Zanzibar. I have collected about 30 processes. The rejected half bore an extraordinary resem- 



specimens and found that they invariably threw off their blance to a nudibranch. The foot was able to adhere and 



tail, at least half the bulk of the entire body, within three the dorsal processes looked like rhinophores. 



f;. TT 71 



