Mr. Alder on the Genus Polycera. 337. 
XXXVIII.— Odservations on the Genus Polycera of Cuvier, 
with Descriptions of two new British Species. By Josuvua 
ALDER, Esq. 
[With a Plate. ] 
In consequence of the small number and rarity of the species 
constituting the genus Polycera of Cuvier, its characters and 
limits are at present very imperfectly understood. I shall, 
therefore, make no apology in bringing under the notice of 
naturalists two or three species belonging or allied to this 
pretty genus, which have lately occurred to me on the coast 
of Northumberland, near Tynemouth and Cullercoates, in the 
hope that the more detailed descriptions and figures which I 
shall be able to give, from having examined the animals in a 
living state, may furnish materials for estimating the value of 
those characters on which a generic distinction ought to be 
founded. 
Cuvier describes the genus as having the branchial plumes 
accompanied by a pair of membranous lamellz capable of 
covering and defending the branchiz in cases of danger*. 
Though the number of these appendages is stated by Cuvier 
to be two, it seems doubtful whether the character of the ge- 
nus should be thus limited. Rang, who had the opportunity 
of examining some exotic species, does not confine his generic 
character to that number, but merely says in his description of 
the branchiz, that “ quelques appendices membraneux les en- 
vironnent.” Without giving any opinion in this matter, it 
will suit my convenience on the present occasion to adopt the 
latter and more enlarged view of the characters of the genus, 
for the purpose of including in it-two new species about to 
be described, which, though they differ in some other respects 
from the typical form, I feel reluctant in the present imper- 
fect state of our knowledge to raise to the rank of genera. 
They constitute, however, two very marked divisions, the 
characters of which may probably afterwards be found of suf- 
ficient value to constitute generic distinctions. Until lately 
the only known British species of this genus was the Doris 
fiava of Montagu, to which Dr. Fleming has added, with some 
doubt, the anomalous Doris pennigera of the same author. 
Neither of these species appear to have been recognized by 
later observers. Very recently the indefatigable researches of 
Mr. Thompson of Belfast have brought to light two other 
British species of this genus, (if, indeed, one of them be not 
* The use here attributed to these appendages appears to be in part, at 
least, imaginary. Such an use is not and cannot be made of them by some 
of the species; their position and small degree of motion preventing their 
being so applied. 
Ann. & Mag. N. Hist. Vol. vi. Z 
