süBCLASs II EUCRÜSTACEA— CIRRIPEDIA 743 



head ; obscurely, and at times not at all segmented ; posterior' portion with at most 

 six pairs of himmous legs or cirri, which^ howevei\ may he fewer in numher or 

 altogether absent. 



The typictal and best known Ciiripedes {Balanidae, Lepadidae) differ so 

 widely from all other Crustacea in their external form, solid calcareous shells, 

 slightly developed respiratory and sensory organs, and especially in their 

 hermaphroditic sexual apparatus, that until 1830 they were commonly classed 

 with the Mollusca. About this time J. V. Thompson and Burmeister showed 

 that these Cirripedes pass through a nauplius stage, and that directly before 

 attachment both Baianus and Lepas undergo a C?/p7S-stage, thus showing very 

 clearly their relation to the Eucrustacea. 



All Cirripedes are marine animals. Those with calcareous shells attach 

 themselves to stones, wood, mollusks, crabs, corals and sea plants, and often 

 Cover rocky coasts in myriad numbers. Some genera {Coronula, Chelonohia) 

 attach themselves to whales and turtles ; some {Pyrgoma, Palaeocreusia) 

 become embedded in corals, and others bore into shells of mollusks or 

 lead a parasitic existence on Decapods or within the shells of other Cirripedes. 

 Most Barnacles inhabit shallow water, but certain genera occur at great 

 depths, from 1900 to 2000 fathoms (Scalpellum, Verruca). Many of the 

 living families are naked, and naturally only those possessing shells 

 (Thoracica) have left fossil remains, although some of the tubulär cavities in 

 molluscan shells may have been perforated by naked Cirripedes. Fossil 

 forms occur sparingly in the older strata, and do not become abundant until 

 near the close of the Tertiary. 



Order 1. THORACICA Darwin. 



Body indistinctly segmented, and enclosed in a membranous mantle in which calcare- 

 ous plates are usually developed. Six pairs of cirri present. Mostly hermaphroditic, 

 sometimes with complemental males. 



The relations of the first two of the foUowing families to the other members of 

 the Order are conjectural. 



Family 1. Lepidocoleidae Clarke. 



Body covered with two vertical coliimns of overlapping plates, those of one series 

 alternating with those of the other. Terminal or caudal plate axial. Basal or cephalic 

 portion of the body with a ventral curvature. Apices of the plates on the dorsal margin. 

 No accessory plates. 



Lepidocoleus Faber (Fig. 1437). Elongate, blade-shaped ; dorsal edge the thicker, 

 ventral edge sharper and linear. The two series of plates niake a complete enclosure, 



on some Fossils of the Cincinnati Group. Journ. Cincin. Soc. Nat. Sei., 1887, vol. ii. — Hall, J., 

 and Clarke, J. M., Palaeontology of New York, 1888, vol. y\\.— Clarke., J. M., Notes on certain 

 .Fossil Barnacles. Amer. Geol., 1896, vol. xwiu— Matthew, G. F., On occurrence of Cirripedes in the 

 Cambrian. Trans. N. Y. Acad. Sei., 1896, vol. xw.—Logan, W. N., Cirripeds from Cretaceous of 

 Kansas. Kansas Univ. Quar. 1897, vol. \\. — Woodward, H., Cirripedes from the Trimmingham 

 Chalk in Norfolk. Geol. Mag. 1906, dee. 5, vol. \n.~Idem, on the genus Laricula. Ibid., 1908, 

 vol. v.—De Alessandri, G., Studi monografici sui Cirripedi fossili d' Italia. Palaeontogr. Ital., 



1906, vol. xii. Idem, Osservazioni sopra aleuni Cirripedi fossili della Francia. Atti Soc. Ital. 



Nat.,' Milano, 1907, vol. \\x.-~Reed, F. R. C, Structiire of Turrilepas and its allies. Roy. Soc. 

 Edinb., 1909, vol. xM. — Withers, T. H., The Cirripede genus Scalpelhim. Geol. Mag. 1910, 

 dee. 5 vol. vii.—Idem, The Cirripede Brachylepas cretacea H. Woodward. Ibid., 1912, vol. ix. 



