NUDIBRANCHIATA. 27 



parting a very peculiar character to the genus. In the 

 Glaucus the branchiae are moulded into fingered fan-like 

 fins ; while in Eolis and Tergipes they form conical or 

 cylindrical papillae, disposed in series along the back 

 and sides/' Dendronotus must surely have been one 

 of the 



" things that are forked and horned and soft," 



which Tennyson's mermaid expected would wait upon 

 her minstrelsy. 



The following descriptive catalogue of the British 

 Nudibranchiate Mollusca was most kindly prepared for 

 me by my lamented friend Mr. Alder ; and it was, I 

 believe, his last scientific work. Being nearly twelve 

 years later than the Monograph, this catalogue is of 

 course more perfect. I have made only a few alterations 

 and additions, the latter being within brackets. In 

 adopting the merger or inclusion of Pellibranchiata as a 

 suborder, I may remark that it is questionable whether, 

 in a physiological point of view, the Nudibranchs ought 

 not to be united with the Pulmonobranchs. The divi- 

 sions founded on the respiratory system are, like many 

 other methods of classification, incomplete and unsatis- 

 factory. An illustration of each family will be given in 

 the plates of genera for this volume. Some of them 

 are taken from the recent work of Meyer and Mobius 

 (' Fauna der Kieler Bucht'), which ought to be consulted 

 by all who study this group. 



