INTEODUCTION. 



The CiRRiPEDiA, both recent and fossil, have been much neglected by systematic 

 naturalists : the fossil species have, however, been more attended to than the recent. 

 Professor Steenstrup has published^ an excellent monograph on the Danish and Scanian 

 Cretaceous species : Mr. J. de Carle Sovverby has given good plates of several British 

 valves in the Mineral Conchology ; and F. Roemer^ has illustrated, by rather indifferent 

 figures, though clear descriptions, various German forms. Other less important notices 

 have appeared by several authors. As yet, however, no monograph has been produced 

 on the whole group. The present volume is confined to the Lepadidce or Pedunculated 

 Cirripedia ; and it so happens that the introduction, under the form of notes, of a few 

 foreign species (which are necessary to illustrate the British species), serves to render 

 this Monograph tolerably complete ; that is, as far as the specimens collected on the 

 Continent (judging from published accounts) serve for this end, — for we shall immediately 

 see that certain valves are requisite in each genus. 



It is unfortunate how rarely all the valves of the same species have been found 

 coembedded ; it is evident that, with the exception of some few species, the membrane 

 which held the valves together, decayed very easily, as it does in recent Pedunculated 

 Cirripedes. Hence, in the great majority of cases, the several valves have been found 

 separate. Hitherto it has been the practice of naturalists to attach specific names 

 indiflerently to all the valves ; and as in each species there are from three to five or six 

 different kinds of valve, there would have been, had not the whole group been much 

 neglected, so many names attached to each species. On the other hand, it has occurred 

 in several instances, that many valves belonging to quite different species have been 

 grouped together under the same name. To avoid these great evils, I have fixed on the 

 most characteristic valves, one in each of the two main genera, and taking them as 



' Naturhistorisk Tidsskrift, af H. Kroyer, 1837 and 1839. 



^ Die Versteinerungen des Norddeutschen Kreidegebirges, 1841. 



