312 Messrs. Alder and Hancock on a new genus and 



and white. Foot nearly linear, transparent white,, the front trans- 

 versely slit and produced at the sides into tentacular points. 

 Length rather more than half an inch. 



From deep water, Torbay. 



This genus belongs to the family of Eolididcej having a ramified 

 digestive system. In general appearance however it greatly re- 

 sembles a Tritonia. It has the same squared or prismatic form, 

 with a pallial expansion down the sides of the back bearing the 

 branchiae, which are papillose and not branched as in that genus. 

 The jaws are large and powerful, resembling those of Eolis, but 

 rather shorter and flatter. The tongue is covered with numerous 

 rows of strong teeth denticulated at the edges. In most respects, 

 the anatomy, as far as it could be made out from a single speci- 

 men imperfectly preserved, agrees pretty nearly with that of Eolis. 

 The principal trunk of the digestive system appears to be follicu- 

 lated and the branches much-divided. The foot, in the only known 

 species, has long tentacular processes, as in several of the Eolides, 

 which it also approaches in the papillose branchiae. We thus find 

 the external characters of the two typical genera of the Tritoniadce 

 and the Eolididce so united in this animal, that were it not for its 

 internal organization, we should have been at a loss in which fa- 

 mily to place it. 



From this circumstance we see the impropriety of dividing these 

 families into separate orders. The anatomy of Dendronotus leads 

 to the same conclusion. This genus, which we have found it 

 necessary to establish in the first part of our ^ Monograph of the 

 British Nudibranchiate Mollusca ' for the Tritonia arborescens of 

 authors, shows the ramifications of the digestive system peculiar 

 to the Eolidida, with a remarkable modification approaching it 

 to the other two families of the order. The follicular portion, 

 instead of being entirely at the extremity of the branches as in 

 Eolis, is principally concentrated round the main trunk, thus re- 

 verting in part to the form of the true liver, and supporting the 

 views of those anatomists who consider the ramifications to be 

 merely modifications of the hepatic ducts. So far, therefore, as 

 the digestive system is concerned, there appears to be no good 

 reason for dividing the order as proposed by M. de Quatrefages; 

 and respecting the vascular system, we have cause for believing 

 that we were correct when we hazarded an opinion that there 

 would be found less difference throughout the order than was 

 supposed. 



We have recently discovered that the Dorides — even the most 

 spiculose — have the whole of the cloak covered with vibratile cilia. 

 From this circumstance alone it might be inferred that the Do- 

 ridida as well as the Eolididce have the blood partially aerated 

 from the general sui-face of the body. This inference however is 



