INTRODUCTION. 7 



from recent forms. It is a rather singular fact, considering the present wide distribution 

 of the genus Lepas or Anatifa, and the frequency of the individuals, that not a single 

 valve known certainly^ to belong to this genus, or to any of the closely-allied genera, 

 has hitherto been- found fossil. 



The oldest known cirripede is, as we have seen, a PoUicipes from the Lower Oolite, and 

 it does not differ conspicuously from some of the recent species of the same genus ; so, 

 again, the cretaceous Scalpellum fossida, and the eocene 8. quadratum are certainly very 

 nearly related to the recent S. rutilum (nov. spec). Loncula alone is a genus perfectly 

 distinct from all living Cirripedia ; and I may here add that of the Tertiary Sessile Cirripedes, 

 I have hitherto not seen a single new generic form. This persistence of the same genera 

 is somewhat remarkable, considering that amongst ordinary Crustacea nearly all the 

 Secondary species belong to extinct genera -^ it should, however, be borne in mind that 

 Limulus has survived from the Palaeozoic period to the present day. The Oolitic, 

 Cretaceous, Tertiary, and recent species of Lepadidse are all different from each other. By 

 looking at the annexed Table, and putting out of question the species of which the age 

 is uncertain, we have five common to two stages of the chalk ; that is assuming for the 

 present that the classification of the stages of the chalk commonly used and here followed, 

 is correct. PoUicipes glaher is common to three, and, I believe, to four stages. Scalpellmu 

 arcuatmn occurs in the Chalk-marl, and upper Greensand, and therefore this species also 

 extends tlu'ough three stages ; but there is a slight difference between the specimens from 

 the upper and lower stages, which some authors might perhaps consider specific. If 

 fossil cirripedia had, like most recent species, very wide horizontal or geographical ranges, 

 then, in accordance with a law now generally admitted, a considerable vertical range in 

 some of the species is not improbable. 



I may here observe that I am assured by Professors Forchammer and Steenstrup, that 

 the formations of Scania and Westphalia are equivalent to that of Faxoe ; and hence to that 

 of Maestricht, I have called these formations the " Maestricht formation," to distinguish 

 them from the common upper or white Chalk. 



1 In a mere catalogue, published without descriptions, in the 'Jahrbuch' for 1831, p. 155, by 

 Hoenninghaus, Anatifa cancellata is given as a tertiary species : Mr. G. B. Sowerby has stated, in his 

 ' Genera of Shells,' that he has seen a Tertiary specimen of this genus, but he cannot remember which 

 valve it was. 



^ Pictet, Traite Elementaire de Paleontologie, torn, iv, p. 4. 



