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 Holidide, 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 bearmg the 
branchie, which are papillose and not branched as in that genus. 
The jaws are large and powerful, resembling those of Hols, 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 Holis. 
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 Holides, 
which it also approaches in the papillose branchie. We thus find 
the external characters of the two typical genera of the Tritoniade 
and the Holidide 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 Holidide, 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- 
ridide as well as the Holidide have the blood partially aérated 
from the general surface of the body. This inference however is 
