4 
2 FOSSIL CIRRIPEDIA. 
typical, have never, except in one instance where several valves were known all to belong 
to the same individual, and in another instance in which a valve was very remarkable, 
attached a specific name to any other one. I have, however, in two cases retained names 
already given to certain other valves, as they presented remarkable characters, and were 
almost certainly distinct. In Scalpellum I have taken the Carma or Keel-valve (7. e. dorsal 
valve of most authors) as typical; and in Pollicipes, the Scuta (7. e. the inferior lateral 
valves of most authors): it would have been desirable to have taken the same valve in 
both genera; but it so happened that the Caria has been much more frequently collected 
than any other valve in Scalpellum, in which genus it is highly characteristic ; whereas 
in Pollicipes, it is apt to present less striking characters than the Scuta, which are, 
moreover, commoner in most collections. In almost all the Lepadidee the Terga (7. e. the 
upper or posterior lateral valves) are not characteristic, and are particularly liable to 
variation. Although only certain valves in each genus thus receive specific names, yet 
from the conditions of embedment, several of the other valves can often be safely 
attributed to the same species. 3 
Much confusion in nomenclature will, I think, be avoided by the plan here adopted ;: 
but the study of Fossil Cirripedia must, I fear, owing to the variability of the valves, as- 
seen in some fossil species, and as inferred from what so commonly occurs with recent’ 
species, ever remain difficult. In very many of those recent species, of which large series 
have passed through my hands, several of the valves have varied so much, that had I 
seen only certain specimens from the opposite poles of the series, I should unhesitatingly. 
have ranked them as quite distinct species: on the other hand there are some recent’ 
forms—for instance, some species of Zepas, and again Pollicipes cornucopia, and elegans 
of Lesson—which are perfectly distmct, but which it would be hopeless to attempt- 
discriminating when fossilized, without quite perfect specimens. It should be borne in’ 
mind, that the recognition of the Fossil Pedunculated Cirripedes by the whole of their’ 
valves and peduncle, is identical with recognismg a Crustacean by its carapace, without’ 
the organs of sense, the mouth, the legs, or abdomen: to name a Curipede by a single 
valve is equivalent to doimg this in a Crustacean by a single definite portion of the’ 
carapace, without the great advantage of its having received the impress of the viscera 
of the included animal’s body: knowing this, and yet often having the power to identify’ 
with ease and certainty a Cirripede by one of its valves, or even by a fragment of a 
valve, adds one more to the many known proofs of the exhaustless fertility of Nature in 
the production of diversified yet constant forms. 
I must allude to one more unfortunate cause of doubt in the classification of the: 
extinct Lepadide, namely, the difficulty in attributing the separated valves to the two. 
main genera of Scalpellum and Pollicipes; for the chief distinction between these two 
close genera in the recent state, lies in the number of the valves, and this can very rarely 
be ascertained in fossil specimens. At first I determined to follow’ those authors who 
have united both genera under Pollicipes; but reflecting that I had twelve recent and 

