16 Couthouy's New Species of Mollusca 
protruded from beneath this cover. Anal orifice slightly 
tubular, situated near the back, between the first and 
second pair of branchie. 
Ozservations. Of the genus "Tritonia, separated by 
Cuvier from the confused genus Doris of previous authors, 
but four or five species were known to him. It has sub- 
sequently been adopted by all zoologists, and the number 
of well established species, augmented to about a dozen. 
Of these, three are from the Red Sea, and the remainder 
are found in the North Sea and British Channel. Those 
inhabiting the Red Sea are eminently distinguished from 
our native species, by having from ten to twelve, in lieu 
of five pair of dorsal branchie ; and, of the rest, one - 
only appears to possess any considerable resemblance to 
it, which is the T. arboréscens, Cuvier. 
The number of dorsal branchie is the same in both; 
and the figure given by Cuvier himself, Ann. du Mus., 
t. vi. pl. 61, fig. 8, 9, 10, has very much the appearance 
of ours when preserved in spirits. He makes no men- 
tion of color, and from his figure and description, we 
may infer that his observations were made upon speci- 
mens in that condition. He describes it as “ T. cor- 
pore oblongo, tumido, branchiis ramosis distinctis, utrin- 
que quinis, posterioribus sensim minoribus, ore quadri- 
lamelloso." Now * corpore oblongo, tumido," is an 
accurate description of our species when observed in 
spirits, but cannot with any propriety be applied to the 
living animal, as may readily be perceived upon a com- 
parison of the specimens in the Society's Cabinet with 
the plates. It is probable, therefore, if it were in our 
power to examine a living individual of 'T. arboréscens, 
it would be found in its general aspect very closely 
allied to our own species. My principal reason for con- 
