172 CIRR1PEDIA. 



abdomen generally rudimentary ; gills, when pre- 

 sent, attached to the under sides of the carapace ; 

 the sexes generally distinct ; the males rudimen- 

 tary and parasitic on the female ; metamorphosis 

 complex. 



Sessile : 



Shell symmetrical ; scuta and terga 

 furnished with depressor muscles ; the 

 other valves united immoveably . . . Balanida. 



Shell unsymmetrical ; scuta and terga 

 moveable only on one side, united on 

 the other side to the external valves . Verrucadae. 

 Stalked Lepadidte. 



Family I. Balanidjs. 



Rostrum with radii, without alee ; lateral 

 valves with aire on one side, and radii on 

 the other ; walls generally porous or inter- 

 nally ridged Balanince. 



Rostrum with alee, without radii ; rostro- 

 lateral valves without alse ; walls not porous CJdhamalina. 



Sub-Family L Balanina. 



Balanus (Ellis). Shell- valves six ; opercular 

 valves sub-triangular. 



B. spongicola. B. crenatus. 

 perforatus. balanoides. 



improvisus. Hameri. 



porcatus. Fig. 320 ; n. s. 



Acasta (Leach). Shell- valves six ; walls and 

 base not porous ; base calcareous, cup-shaped ; 

 affixed to sponges, or to the Isis corals. 



A. spongites. Fig. 321 ; ?i. s. 



