THE CIRRIPEDIA 



109 



C.L. 



FIG. 58. 



Turrilejyas Wrightii. 



a portion i further enlarged. C, carinal scales ; 



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 Turrile])as WrightiL A , view of the whole fossil. 



side of the Capitulum is Called B, a portion! further enlarged. C, carinal scales ; 

 , , ., C.L, cari no-lateral ; L, lateral ; R.L, rostro-lateral ; 



the "rOStral, the Opposite A', rostral. (From Gnivel's Monographic.) 



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 Tunilepas (Fig. 

 58) from Silurian and 

 Devonian rocks, in which 

 the whole animal appears 

 to be covered with im- 



Loriritln pnl-heUn. C, carinal scales ; C.L, carino- Itripotirur cralp arr-ino-prl 



lat.-r.il; /./lateral; ILL, mstro - lafral ; *, rostral. p ncatm g SCale& arranged 



Tin; capitular plates are not correctly shown. (From in transverse TOWS of five 



(iruvel s Muuuyniiihie.) , . , m i 



on each side. Ine genus 



Lnricala (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 Turrilcpas. At one end of the- animal, several 



C.L. 



R.L. 



