92 CRUSTACEA——CIRRIPEDIA CHAP. 
in the skin of whales, the shell of the first-named being of a 
highly compheated structure with hollow triangular compartments 
into which the mantle is drawn out. 
Xenobalanus globicipitis lives attached to various Cetacea, 
and is remarkable for the rudimentary condition of its skeleton, 
the six plates of which form a mere dise of attachment from 
which the greatly elongated naked body rises, resembling one of 
the naked Stalked Barnacles. 
Fam. 4. Tetrameridae.—In this family only four skeletal 
plates are present (Fig. 65, C). This family is chiefly confined 
to tropical seas or those of the Southern hemisphere. The chief 
genera are Tetraclita and Pyrgoma, found in British seas. 
Sub-Order 3. Acrothoracica. 
Gruvel includes in this sub-order four genera (Alcippe, 
Cryptophialus, Kochlorine, and Lithoglyptes), the species of 
Fic. 64.—Alcippe lampas. A, 9, x about 10, seen from the right side, with part of the 
right half of the animal removed ; B, dwarf male, x about 30. A.J, adductor muscle ; 
An, antenna; ©, 1st pair of cirri; Cr, posterior thoracic appendages ; H, eye; G, 
testis; M.C, mantle-cavity; O, ovary; P, penis; 7, penultimate thoracic seg- 
ment; V. vesicula seminalis. (After Darwin.) 
which live in cavities excavated in the shells of molluscs or in 
the hard parts of corals. 
Darwin discovered and described Cryptophialus minutus, and 
placed it in a sub-order Abdominalia, believing that it was 
