Introduction to Animal Morphology. 345 



five calcareous plates, one dorsal, azygos (carina), two large, 

 lateral, anterior (scuta), and two, small, posterior (terga} ; an 

 adductor muscle is attached to the scuta, but all are separately 

 movable on each other. Sometimes these pieces may be far 

 removed from each other, and small (Otion), reduced to 

 two, or even no calcified plates may exist (Anelasma), or the 

 plates may be 20-100, the five principal being detectible 

 (Pollicipes), or 15-20, indistinguishable (Scalpellum, the 

 males of this form have 2-4, the females 15-20 pla: 

 2. Balanidas sessile, conical or cylindroidal, on a calca- 

 reous basis, which has the ovary and cement gland be- 

 tween its lamellae ; shell-pieces, 4-8, immovable in a circle, 

 whose posterior (upper) opening is closed by a retractile 



"culum of two pairs of plates (scuta and terga), moved 

 I>\ adductor and depressor muscles. In this shell the lepa- 

 dine carina forms an annular wall, within which the scuta and 

 terga are prolonged, their posterior ends forming an opercu- 

 lum. The annular wall consists of two symmetrical, lateral 

 s (carina and ros/rum), with a thin, outer (radius], or 

 inner (aid) lateral process ; between the carina and ros- 

 trum there may be one pair of lateral plates, or two pair 

 (rostro-lateral and carino-lateraT). The rostrum sometimes 

 has an ala, with a test of six (Chthalamus) or eight plates 

 (Octomeris). The rostrum in others has a radius, and 

 the shell may be all of one piece (Pyrgoma), or of four 

 vertical plates (Tetraclita), or six, as in lialanus, or in the 

 whale oikosite Coronula. 3. Verrucidae scuta and ter-a 

 with no depressor muscles, movable at one side ; on the 

 other fused with the rostrum and carina. 



2nd. Abdominalia (Darw in) mantle compressed, conical, 



with a lateral opening (AlcippiO, or ila^k-like, \\ith terminal 



opening (Cryptophialus) ; with n<> calcareous plates, but with 



a l>mad adhe : body, at least for its hinder part, se^- 



: labrum long, movable ; cirri abdominal, three )>air; 



ions, with pigrm hich two are attached to 



female. 



3rd. Apoda(/ -mantle filamentary ; mouth si: 



rial; body imprr:"- with no cirri. tCO- 



