2 FOSSIL CIRRIPEDIA. 



typical, have never, except in one instance v^^here 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 Carina or Keel-valve (?'. e. dorsal 

 valve of most authors) as typical ; and in PolUcipes, the Scuta (^. 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 Carina 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 Lepadidse the Terga (?'. 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. 



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 tlu-ough 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 Lepas, and again Pollicipes cornucopia, and elegans 

 of Lesson — which are perfectly distinct, 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 recognising a Crustacean by its carapace, without 

 the organs of sense, the mouth, the legs, or abdomen : to name a Cirripede by a single 

 valve is ecjuivalent to doing 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 Lcpadidae, 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 



