NUDIBRANCHIATA. 551 



in which the mantle is extended. Thorunna, Bgh., closely resembles Chromodons, but lacks 

 the labial armature. 



The Chromodorids are confined to the warmer seas, and are most abundant in the 

 Tropics, but there are some ten species in the Mediterranean, and the genus is represented 

 on the coasts of Japan and California. They are common on coral reefs and in pools filled 

 with seaweed. Their brilliant coloration, which is often dazzlingly gorgeous in the living 

 animal, does not appear to in any way harmonize mth their environment. On the other 

 hand some of the most striking species are commonly found under stones where their hues 

 can be neither " protective " nor " warning." 



The species of Chromodoris are distinguished largely by their colour, though other 

 characters are not wanting, such as the details of the teeth and labial aruiature, the presence 

 of rhachidian thickenings, glands on the mantle edge, and the arrangement of the gills. 

 The number of gills hoAvever is not constant in the same species, and even the arrange- 

 ment seems to vary. The colour of Nudibranchs as a rule is very variable, but in this 

 genus the general pattern and ground colour, though they may differ in elaboration or 

 intensity, are mostlj- constant. Unfortunately there are no notes as to the living colours of 

 the specimens in this collection, and in only two are they recognisable, so that it is 

 exceedingly difficult to make any certain identifications. 



8. Cla: elizabethina Bgh. 



Two specimens from S. Nilandu Atoll, Maldives, 30 /. One was dissected. The animal 

 was much bent, but if straightened out would have been about 2'5 cm. long by '6 broad. 

 Colour in alcohol brownish-j^ellow, margin of mantle whiter. From a black patch between the 

 rhinophores rise three broad black lines, two of which run down the sides and meet behind 

 the gills, while the third runs from the rhinophores to the anterior edge of the branchial 

 pocket. Round the sides of the body are other black lines, in one specimen three, in the 

 other two. In this latter specimen the lines are only on one side, having disappeared on 

 the other. Branchiae twelve, two being free in the middle, and the rest united at theii- 

 bases into two groups of five, one on each side. Three gills on one side and two on the 

 other were bifid. The radula with thickenings on the rhachis: the innermost teeth with 

 4 small denticles on each side. The outermost with from 2 to 4 points. 



9. Ghr. rosans B. (? Chr. Bidlockii Coll.). 



One small specimen fi-om Minikoi. 1-3 cm. long and "5 broad. Colour a uniform reddish- 

 purple, with traces of a white border. Rhinophores and branchiae grey. It would appear that 

 the living animal is rose-coloured, with a brilliant white border and yellow rhinophores 

 and branchiae. Gills nine, apparently set in a horseshoe open behind, decreasing in size 

 as they go backwards. No thickenings or rhachis of radula: teeth as usual, outermost with 

 several largish denticles. 



This seems to me to be a young individual of Chr. rosans B., which is probably identical 

 with the Chr. Bidlockii described and figured by Collingwood {I. c). 



10. Chr. pustulans B. 



Two specimens from Minikoi seem referable to this species. Length of largest 2'1 cm., 

 breadth 1"2. The broad back is covered with low, round tubercles. The gi-ound colour is dull 

 yellowish-brown, but the gills and tubercles show traces of bright yellow pigment. The 



