152 ANNULOSA. 



As regards the distribution of the Balanida in time, the 

 oldest known representative of the family, so far as is certainly 

 known, has been indicated by Mr Seeley as occurring in the 

 Lias, and has been made the type of a new genus under the 

 name of Zoocapsa. So far as is known, no member of the 

 group occurs in any Palaeozoic deposit ; and negative evidence 

 is in this case of considerable value, as the Balani possess a 

 shell which is readily preserved, whilst they adhere to all 

 sorts of marine bodies. With the above-mentioned exception 

 (which may, perhaps, be referred to the Verrucidce), no fossil 

 Balanoid has hitherto been discovered in sediments older 

 than the commencement of the Tertiary period. The genus 

 Balanus is the earliest of the group, and appears under several 

 specific forms in the Eocene Rocks. In the Miocene and 

 Pliocene deposits, the Balanidce are abundantly represented 

 by Balanus itself, and in the latter by the genera Acasfa, 

 Pyrgoma, and Coronula. 



The remaining family of the Sessile Cirripedes is that of the 

 Verruridce, comprising only the single genus Verruca. In many 

 respects the Verrucida approach the Balanidce, but the shell is 

 composed of six valves only, and is unsymmetrical, whilst the 

 scuta and terga (forming the operculum), though movable, 

 are not furnished with a depressor muscle. The Verrucida 

 appear, so far as is known, to have commenced their existence 

 towards the close of the Secondary period, the Chalk having 

 yielded one species. Verruca Stromia is found in the Coralline 

 and Red Crags (Pliocene), in Glacial deposits, and in existing 

 seas. 



The third family of the Cirripedia Thoracica is that of the 

 Lepadidce or Pedunculated Cirripedes, commonly known as 

 " Barnacles." In these (fig. 97) the animal differs from the 

 Sessile Cirripedes in having its anterior extremity greatly 

 elongated, forming a stalk or " peduncle " by which the animal 

 is fixed to some foreign object. At its free extremity the 

 peduncle bears the "capitulum," which corresponds to the 

 shell of the Balanoids, and is composed of various calcareous 

 pieces, united by a membrane, moved upon one another by 

 appropriate muscles, and protecting in their interior the body 

 of the animal with its various appendages. The peduncle is 

 cylindrical, of varying length, flexible, and furnished with pro- 

 per muscles. In some species the peduncle is naked, and can- 

 not be preserved in the fossil condition ; but in other cases 

 the peduncle is furnished with calcareous scales (Loricula and 

 Turrilcpas, fig. 99), in which case it is readily preserved. The 

 " capitulum " (fig. 98), as before said, corresponds with the 



