100 MICROSCOPICAL STUDIES. 



Tribe I. PEDUNCULATA ; stalked, six pairs thoracic limbs. 



Families. Lepadidw (stalks without calcareous plates or 

 hairs) ; and PoUic&pedidce (stalks with hairs or 

 plates). 



Tribe II. OPERCULATA ; sessile, limbs same as in Peduncidata. 

 Families. Balanidce and Chthamalidce (closely related, 

 both with a symmetric calcareous ring, each 

 branchia a single fold) ; Coronulidcc (symmetric 

 ring of plates, each branchia doubly folded) ; Ver- 

 rucidce (calcareous ring asymmetric). 

 Tribe III. ABDOMINALIA ; thorax reduced, bearing three pairs 



of cirri form limbs. 

 Family I. Alcippidce, four pairs thoracic limbs, three 



pairs being cirriform. 

 Family II. Cryptophialidce, three pairs only of thoracic 



appendages all cirriform. 

 Tribe IV. A POD A ; no thoracic limbs, grub-like. 



Family. Proteolepadidcc. 



Sub-Order II. Rhizocephala ; parasitic body sac-like without 

 mouth or alimentary canal ; possessing root-like 

 processes that ramify in the viscera of the host. 

 One family only. Kentrogonidce. The chief genera are 

 Peltogaster, parasitic on Hermit Crabs, and Sac- 

 culina, parasitic on Cancer, Carcinus, &c. 



