Introduction to Animal Morphology. 345 



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

 lateral, anterior [scuta), and two, small, posterior {ierga) ; 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 plates). 

 2. Balanidae — 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 

 •operculum of two pairs of plates (scuta and terga), moved 

 by 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 w^all consists of two symmetrical, lateral 

 pieces {carina and rostrum), with a thin, outer {radius), or 

 inner {ala) lateral process ; between the carina and ros- 

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

 {j-ostro-lateral and carino-lateral). 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 Balanus, or in the 

 whale oikosite Coronula. 3. Verrucidae — scuta and terga 

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

 other fused with the rostrum and carina. 



2nd. Abdominalia {Darwin) — mantle compressed, conical, 

 with a lateral opening (Alcippe), or flask-like, with terminal 

 opening (Cryptophialus) ; with no calcareous plates, but with 

 a broad adhesive disc ; body, at least for its hinder part, seg- 

 mented ; labrum long, movable ; cirri abdominal, three pair ; 

 dioecious, with pigmy males, of which two are attached to 

 each female. 



3rd. Apoda {Dai-witi) — mantle filamentary ; mouth sucto- 

 rial ; body imperfectly segmented, with no cirri, ex. Proteo- 

 lepas. 



