84 



CRUSTACEA — CIRRIPEDIA 



Sub-Order 1. Pedunculata. 



Til this division, sometimes combined witli the Operculata 

 as TnORACiCA, owing to the extremely reduced state of the 

 abdomen, the body is borne on a distinct stalk, and the bivalve 

 arrangement of the mantle is clearly retained. The mantle is 

 protected externally by a numl)er of calcareous plates, the 

 arrangement of which is typical of the various genera. It 

 appears that in the most primitive and geologically oldest 

 Cirripedes, the probable ancestors of the Pedunculate and Oper- 

 culate sub-orders, the arrangement of the plates was somewhat 

 irregular, and they were far more numerous than in the modern 

 forms, so that passing from these older types to modern times 

 we witness a reduction in the number and a greater precision 

 in the arrangement of the skeletal parts. 



One of the most ancient Cirripedes known is Turrile2')as, which 

 occurs in the Silurian deposits of England, but it is also known 

 /^ from earlier deposits, while undoubted 



Cirripedes ha^■e been found in the Cam- 

 brian of North America. The body of 

 T'urrilejms is enclosed in imbricating 

 plates, as shown in Fig. 53, A. 



In Archaeolepas of the Upper Jurassic 

 (Lithographic slates of Bavaria) the ar- 

 rangement of scutes typical of the Lepa- 

 didae is foreshadowed, but the whole 

 of the peduncle is protected by rows 

 1 ; B, Archaeolepas redten- of plates (Fig. 53, B), as in Turrile'pas. 



hacheri (Jurassic), x 1. C, 

 carina ; R, rostrum ; S, 



A B 



Fig. .53. — A, Turrihpas 

 wrightianus (Silurian), 



The above-mentioned senera did not 



scutum ; T, tergum. (After survive luto the Cretaceous period, their 

 Zittel.) , , . , , - -r, 7, . • 



places being taken by the genera loUmpes 



and SealpeUum, which first appeared in the Silurian and persist to 



the present time, the older and more primitive FoUicipes being 



represented by about half a dozen living species, while the species 



( >f ScalpeJlum are exceedingly numerous. 



Fam. 1. Polyaspidae. — This family includes the three genera, 

 FoUicijjes, Scalpcllam, and Lithotrya. 



Polliciiies is not only very ancient geologically (being found from 

 the Ordovician upward), but it preserves the primitive character- 



