70 
upturned side lobes were coloured exactly like the sand, while the 
dark green dorsal surface was totally concealed by the lobes. This 
case, though perfect enough, is, however, only a variation of the 
usual adaptation of the sand fauna. 
For the rest I would say that some of the cases of protective 
resemblance in Nudibranchs quoted in litterature do not appear 
Fig. 5. Xenophora sp. Nat. size. 
to me very convincing — so far as I have had opportunity of 
seeing them in nature —- f. i. that Æolis papillosa should re- 
semble a contracted Sagartia troglodytes (Plateau, p. 107). I am 
inclined to agree with M'Intosh in his more critical view of pro- 
tective or warning coloration in Nudibranchs. 
Upon the whole the Molluscs afford only few instances of pro- 
tective adaptation; besides the above mentioned Cypræa, so far as I 
know, Ovulum and Lamellaria (Plateau, p. 103) are the only 
good cases of protective resemblance, known among them. Even 
cases of adventitious protection are rare, although we have in 
Xenophora one of the very finest examples of this sort of protect- 
ive adaptation known at all. Fig. 5 represents a species of Xeno- 
phora, which, so far as I have had the opportunity to see, has 
aquired the most perfect protection even among Xenophoras. It was 
found off Jolo on a bottom of coral pebbles and Lithothamnia, in 
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