446 CRUSTACEA. 



2. Operculata. The peduncle is absent or rudimentary. The 

 body is surrounded by an external ring of plates at the extremity of 

 which the scuta and terga form an operculum, which is usually freely 

 movable and provided with depressor muscles (fig. 3-48, b}. 



Fam. Balanidae. Scuta and terga freely movable and articulating with one 

 another. The gills are formed each of a fold. Balanus tlntlnnalulum L. 

 Widely distributed and found in a fossil form. B. improvims Darw. Found in 

 brackish water. 



Fam. Coronulidae. Scuta and terga freely movable, but not articulating 

 with one another. The two gills formed each of two folds. Tvbicinella 

 tracltcalis Shaw., South Sea. Coronula "balcenarls L., Antarctic Ocean. C. 

 tliadema L., Arctic Ocean. 



3. Abdcminalia. The irregularly segmented body is enclosed in 

 a flask-shaped mantle, and bears on its terminal portion three pairs 

 of cirriforrn feet. Mouth parts and alimentary canal completely 

 developed. The sexes are separate. They live as parasites buried 

 in the calcareous shell of Girripedia and Mollusca. 



Fam. Alcippidae. With four pairs of feet, of which the first pair is palpiform, 

 and the two last are uniramous and composed of few elongated joints. The 

 sexes are separate. The female bores into Mollusc shells. The male is dwarfed, 

 and is without mouth, stomach, or feet. Alcqipc laj>ij>as Hanc., bores into 

 the columella of the shells of fusus and Buccimim. Found on the coast of 

 England. 



Fam. Cryptophialidae. They have three pairs of feet at the posterior end of 

 the body. Crypioplualus Darw., sexes separate. Or. muivtus Darw., in the 

 shell of Concholepas Pcruviana, found on the west coast of South America. 

 Koclilorine liamata Xoll, lives in excavations in the shell of ILalwtis. 



4. Apoda. The body is segmented, and is composed of eleven 

 rings. There is no special reduplicature of the mantle. The shape 

 resembles that of a maggot. The attaching antennae are elongated 

 to the form of a band. The mouth is adapted for sucking, and has 

 mandibles and maxilla?. Feet absent. The digestive canal is rudi- 

 mentary. They live parasitically in the mantle of other Cirripedia. 

 They are hermaphrodite. 



Fam. Proteolepadidae with the single genus Protcolcjtas Darw., Pr. M-vincta 

 Darw., West Indies. 



5. Rhizocephala* (Suctoria). Body tubular or saccular, without 

 segmentation or appendages; with narrow, short peduncle for 

 attachment, from which branched, root-like filaments arise. The 



* W. Lilljeborg, "Les genres Liriope et Pcltogaster," Nova act a, rrtj. .we. 

 acii'ii. UpsaL, Ser. 3, vol. Hi., 1S(>0. Fr. Mliller. " Die Rhizoccphalen," Archiv 

 fur Naturgeach.. 1862 and 1863. R. Kossmann, ' Beitriige zur Anatomic der 

 schmarotzenden Rankenf ussier," Vcrh. dcr med.-phys. Gesdlsch, Wurzburg, 

 Ncuc Folge, Tom. IV. 



