THE CIRRIPEDIA 



109 



C.L 



Fio. 5f>. 



ll.L. 



Turrilejia.f Wriiihtii. A, view of tin; whole fossil. 



a flattened disc of attachment, as in the OpeicuLita and Acrothoracica. 

 "When a peduncle is present, the rest of the body enclosed by the 

 mantle is distinguished as the capitnlmn. 



On account of the confusion which Avould arise from applying 

 the usual terms of orienta- 

 tion to animals of such com- A B 

 plex form, it is customary, 

 in describing Cirripedia, to 

 employ an arbitrary termin- 

 ology in which the animal 

 is supposed to be placed 

 vertically with the capitulum 

 above, and the peduncle or 

 base of attachment below. 

 What is, morphologically, 

 the sternal aspect of the 

 peduncle and the anterior 



side of the capitulum is called B, a portion 1 furtiier eniarged. C, carinal scales; 

 ,, ,, , •.,, ,, ., C.I,, cariiio-lateral ; /,, lateral; li.L, rostro-lateral ; 



the rostral, the opposite /.>, rostral. (From Gruvel'.s MoHogm-phie.) 



being the " carinal " side. 



The number and arrangement of the calcareous plates on the 

 outer surface of the body afibrd valuable systematic characters, 

 throwing light on the phylogenetic history of the group. It seems 



probable that in the most 

 primitive Cirripedia there 

 was no distinction of capit- 

 ulum and peduncle, the 

 ■whole body l)eing en- 

 veloped by a mantle, 

 probably bivalved, and 

 7> strengthened with shelly 

 plates. Such a form i& 

 perhaps represented by 

 the fossil Turrilepas (Fig. 

 58) from Silurian and 

 Devonian rocks, in which 

 the whole animal appears 

 Fi"^-- 51). to be covered with im- 



Loricida pu^chelh. C, carinal scales ; C A, carino- bHcatiug SCalcS arranged 



lateral; L, lateral; Jl.L, rostro-lateral; B, rostral. . * o^^ 



The capitular plates are not correctly shown. (I'roni in tranSVCrSC TOWS of five 

 Gruvel's J/o«o(7/Yn</4ie.) , .1 rni 



on each side, ihe genus 

 Loricula (Fig- 59), appearing in the Lower Cretaceous, has been 

 supposed to represent the next stage of evolution, showing the 

 beginning of the differentiation between peduncular and capitular 

 plates. In the peduncular region the arrangement of the plates 

 is the same as in Turrilepas. At one end of the animal, several 



