A MONOGRAPH 



BRITISH NUDIBRANCHIATE MOLLUSCA. 



The Mollusks whose history and characters it is the purpose of the present work to 

 illustrate, form an attractive group of the class Gasteropoda, until lately little noticed, and 

 supposed to be of small extent, but which modern researches have brought into more 

 prominent importance. 



As here treated of, the order Nudibranchiata is restricted to those animals bearing 

 the character assigned to it by Cuvier; namely, the possession of distinct external and 

 uncovered gills. This group forms the family Tritoniens of Lamarck. Blainville has made of 

 it two orders, — PolybrancMata and Cyclobranchiata ; and in the more recent arrangement of 

 Milne Edwards, it constitutes a family of his Opistobranchiata. 



The Nudibranchiate Mollusca are all marine, and, with the exception of a few species, 

 are of small size. To some they are known by the familiar name of sea-slugs ; a name, 

 however, not exclusively applied to them, as it is given to several other naked mollusks, 

 which, like them, have a resemblance to the land slugs in the general form of their body. 

 The term, as applied to these animals, is far from complimentary. The land slugs are 

 generally sombre in colour, and plain and uninviting in form, while these little; inhabitants of 

 the deep are often adorned with the most brilliant colours, and of forms the most varied and 

 graceful. 



Their body is usually elongated, soft, and attached through its whole length to the foot 

 or disc upon which they crawl. It is not unfrequently covered with a cloak, and in the 

 family Dorididce the skin is strengthened with calcareous spicula. 



The head is anterior, and frequently indistinct, bearing one or two pairs of tentacles, the 

 upper pair of which are placed on the cloak when it is present, and behind them the eyes are 



1 



