INTRODUCTION. 
Tse Cirripepra, 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 Sowerby 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 Lepadide 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 
indifferently to all the valves; and as im 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. 

