THE CIRR1PED1A 



109 



R.L. 



FIG. 58. 



Turrileiius H'rii/htii. A, view of the whole fossil. 

 B, a portion further enlarged. (', carinal scales ; 

 C.L, cariuo-lateral ; L, lateral ; R.L, rostro-lateral ; 

 the Opposite j;, rostral. (From Gravel's Monographic.) 



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

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

 mantle is distinguished as the capitulum. 



On account of the confusion which would arise from applying 

 the usual terms of orienta- 

 tion to animals of such com- 

 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 

 the "rostral, 

 being the " carinal " side. 



The number and arrangement of the calcareous plates on the 

 outer surface of the body afford 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 being en- 

 veloped by a mantle, 

 probably bivalved, and 

 strengthened with shelly 

 plates. Such a form is 

 perhaps represented by 

 the fossil Turrilepas (Fig. 

 58) from Silurian and 

 Devonian rocks, in which 

 the whole animal appears 

 to be covered with im- 



C, carinal scales ; C.L, carino- b r i ca ting Scales arranged 



lateral ; L, lateral ; 7,'. /,, rostro - lateral ; S, rostral. . B 



Th-' i-apitular plates are not correctly shown. (From m transverse TOWS of five 

 Gruvel's Moiinn-raiihie.) i -j rr>i_ 



on each side. Ihe genus 



Loriculu (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 



C.L. 



L. 



FIO. 59. 



