294 LECTURE XIII. 



multiarticulate, attached to the hinder end of the abdomen. No 

 oviducts. Metamorphosis and metagenesis resulting in a permanent 

 parasitic attachment of tlie fully developed female or hermaphrodite 

 individual. 



Order I. Thoracica. 



Carapace, either a capitulum on a pedicle, or an operculated shell 

 with a basis. Body, formed of six thoracic segments, generally 

 furnished with six pairs of cirri ; abdomen rudimentary, but often 

 bearing caudal appendages ; mouth with labrum not capable of inde- 

 pendent movements ; larva, first one-eyed, with three pairs of legs ; 

 lastly two-eyed, with six pairs of legs. 



Sub-order Balanid^e. (Acorn-shells.) 

 Sessile, or without a peduncle : scuta and terga' provided with 

 depressor muscles : the rest of the valves immoveably united 

 together. 



Family BalanincB. 



Shell, with the rostrum having radii, but without alae ; lateral 

 compartments all having alae on the one side and radii on the other 

 side. Mouth, with the labrum notched in the middle, not tumid ; 

 palpi large, almost touching each other ; mandibles generally with 

 the lower teeth laterally double; third pair of cirri with their segments 

 resembling those of the second pair. 



A. Scutum and tergum articulated together, or overlapping each 

 other ; each branchia composed of a single plicated fold. 



Genera Balanus, Acasta, Elmijiius, Tetraclita, Pyrgoma, Creu- 

 sia, Chelonohia. 



B. Scutum and tergum (when both are present) not overlapping 

 each other ; basis membranous ; parietes often deeply folded, with 

 the outer lamina, towards the basis, generally imperfect; each 

 branchia composed of two plicated folds ; shell attached to living 

 vertebrata. 



Genera Coronula, Platylepas, Tubicinella, Xenobalanus. 



Family Ctham,alinoB, 



Shell, with the rostrum having alee, but without radii, rostro-lateral 

 compartments without alae on either side ; parietes not porose. 

 Mouth, with the labrum bullate ; palpi hardly touching each other : 

 third pair of cirri with the segments resembling those of the fourth 

 pair. 



Genera Cthamalus, Chamcesipho, Pachylasma, Octomeris, Cato- 

 phragmifs. 



