C1RRIPEDTA. 425 



male in 19, confirming the results which Darwin arrived at on much 

 more meagre material. 



Tribe 2. OPERCULATA. The peduncle is rudimentary or absent. 

 The body is surrounded by a ring of plates (testa) the entrance to which 

 can be closed by the scuta and terga which together form an operculum 

 and (except in Verrucidae) are provided with depressor muscles. 



Fam. 1. Coronulidae. Scuta and terga when present freely movable, 

 but not articulating together. Rostrum overlapping the adjacent plates 

 laterally. Base of the shell membranous. The paired branchiae each 

 consist of two folds. On cetacea and other pelagic vertebrates. Coronula 

 Lam., attached to the skins of cetacea. Testa not so high as it is broad ; it 

 consists of 6 similar broad pieces of shell the walls of which are thin and deeply 

 folded, the cavities of the folds are turned towards and are filled by the 

 epidermis of the host ; terga and scuta small, not filling the aperture of 

 the testa ; three species. Platylepas Gray, resembling Coronula, but the 

 pieces of the shell are bilobed ; in the warmer seas, attached to turtles, 

 sea-snakes and manatee. Tubicinella Lam., testa much higher than it is 

 broad, formed of six amalgamated pieces ; these basket-like cirripedes 

 are embedded in the skins of whales in the S. Ocean, often associated 

 with Coronula balaenaris. Stephanolepas Fischer, on Chelone imbricata. 

 Xenobalanus Steenstr., shell a shallow six-rayed ring embedded in the 

 superficial layers of the skin of the porpoise on which this cirripede lives ; 

 the body is much elongated (nearly 2 inches), and externally resembles one 

 of the Pedunculata, only the base of it being contained in the shell ; it 

 consists however of the elongated mantle the cavity of which extends 

 down to the cavity of the shell ; the margins of the aperture are reflexed 

 forming a collar, and there are no shell plates ; N. Atlantic. 



Fam. 2. Balanidae. Scuta and terga freely movable, and articulating 

 with one another. The paired branchiae each consist of a single fold with 

 subordinate lateral folds. Balanus Lister, testa cylindrical or conical, 

 consisting of 6 pieces ; from the upper limit of the tidal zone to 50 fms., 

 in arctic to tropical seas throughout the world ; 41 species. Acasta 

 Leach, lives attached to sponges. Tetraclita Schum., testa composed of 

 four pieces (carina, rostrum and 2 lateral) permeated by pores ; T. 

 porosa GmeL, the number of segments in the cirri is very variable. 

 Elminius Leach, testa composed of four pieces not porous. Pyrgoma 

 Leach, testa formed of a single piece ; the scutum and tergum of each 

 side are more or less completely joined together. Lives embedded in 

 corals, chiefly in tropical seas. Creusia Leach, like Pyrgoma, but the 

 testa consists of four pieces. Chelonobia Leach, testa of 6 pieces, one 

 of them consisting of the rostrum and two rostro-lateral elements united 

 together. The pieces are thick -walled and not infolded from the base ; 

 scuta narrow united to the terga by a horny articulation ; attached to 

 turtles, Crustacea and smooth gastropod shells, throughout the warmer 

 and tropical seas. 



Fam. 3. Chthamalidae. Rostrum overlapped laterally by the ad- 

 jacent plates. Chthamalus Ranz., Chamaesipho Darw., P&chylasma 

 Darw. found in deep water. Octorner'is Sow., testa formed of 8 pieces. 

 Catophragmus Sow., testa formed of 8 large pieces, with imbricated series 

 of smaller plates set round about them, becoming smaller towards the 

 base. Littoral ; W. Indies and Australia. 



Fam. 4. . Verrucidae. Scuta and terga without depressor muscles. 

 Those of one side only (right or left) move freely, their fellows having 



