CRUSTACEA. 



153 



shell of the Balani, and is generally much flattened. It con- 

 sists ordinarily of five or more valves united to one another 

 by membrane, usually with marked interspaces ; but the valves 

 may be rudimentary or wanting, and 

 the entire capitulum may be mem- 

 branous. The parts of the capitu- 

 lum correspond ideally with the parts 

 of the shell in the Balanoids. In 

 the latter, however, the shell is for 

 the most part composed of the " com- 

 partments," and the " operculum " is 

 comparatively small and insignificant. 

 In the Lepadoids, on the other hand, 

 the valves which correspond with the 

 operculum of the Balanoids are dis- 

 proportionately developed, and the 

 valves which correspond with the 

 compartments of the Balanoids are 

 much less conspicuous, and are often 

 partially absent. The most important 

 and persistent of the valves are the 

 "scuta" (fig. 98, b], which protect the 

 front part of the body, and correspond 

 with the valves bearing the same name 

 in the operculum of the Balanoids. 

 The next most important are the 

 " terga" (fig. 98, a), which protect the 

 dorso-lateral surface. A pair of scuta 

 and a pair of terga are present, and 

 these are the largest of all the valves. 

 The " carina " and " rostrum " are 

 placed along the edges of the capitu- 

 lum, the former being much the most 

 important, and there may be a " sub- 

 carina " and " sub-rostrum." The re- 

 maining valves, with the carina and 

 rostrum, correspond with the proper 

 shell of the Balanoids ; but they are often wanting or rudi- 

 mentary, and they require no further consideration here. 



As regards the distribution of the Pedunculated Cirripedes 

 in time, until recently no member of the family was certainly 

 known to have existed in the Palaeozoic period. Mr Henry 

 Woodward, however, has described a very interesting form 

 from the Upper Silurian Rocks, under the name of Turrilepas 

 (fig. 99, A). In this singular fossil the peduncle was furnished 



Fig. 97. Anatifa lepas, a 

 recent Pedunculated Cirripede. 

 The lower figure shows the 

 scutum detached. 



