746 



AETHROPODA 



PHYLUM VII 



Family 5. Verrucidae Darwin. 

 Shells sessile and composed of six pieces. Of the scuta and terga only those of one 



side are free the others heing fused with the rostrum or canna. 



The solitary genus Verruca Sclium., ranges from tlie Cretaceoiis to Recent. 



Family 6. Balanidae Darwin. (Acorn Barnacles). 



Shell ohtusely conical, cireular or oval in cross section, with hroad, offen calcareous 

 and cellular hase ; composed of four to ten '' compartments" more or less completely fused 



at their sides, and two pairs of free terga and scuta 

 which dose the upper aperture like an operculum. 



Of tlie lateral plates whicli compose the crown- 

 shaped immovable test, two are designated as carina 

 AB c 



Fig. 1446. 



Diagram of the sliell of Baianus. B, 

 Basis ; C, Carina ; CL, Carino - lateral 

 compartment ; L, Lateral compartinent ; 

 R, Rostrum ; RL, Rostro-lateral com- 

 partment. Each valve or "compart- 

 ment" consists of a central "paries" (p) 

 flanked by "alae" (a) or "radii " (r). 



Fig. 1447. 



Scutum and tergum of Baianus. A, External aspect of tergum, 

 sliowing "spur" below and "beak" above. B, Internal view of 

 scutum, showing muscular scar (x). C, Internal view of tergum 

 (after Darwin). 



and rostrum, the pieces lying between and occurring in pairs being called lateralia. If 

 ^ ;. additional plates are inserted 



among the lateralia, they are 

 termed according to their position 

 rostro- or carino - lateralia. The 

 scuta and terga lie free oii the 

 back of the aniinal, and in fossil 

 forms are generally lost. They 

 have a very characteristic form, 

 and hence are of great systematic 

 importance. Since among fossil 

 species, however, only the mar- 

 ginal plates are for the most part 

 preserved, the determination of 

 their structural characters is often 

 quite uncertain. 



Baianus Lister (Figs. 1446- 

 ,. j . , i p . 1449), Shell low, conical or 



cyhndncal, composed of six pieces. Opercular plates sub-triangiüar ; base membranous 



or calcareous. Eocene to Recent. 



Protohalanus Whitf. Affinities doubtful. Composed of twelve plates, of which 



bas^"^ MWdL dIvoS ''''*'''"' ''^^^^' ^""^''^^'^ '"^ ^^^ ^^^^ ^'''^^ ^^^^ ^'^' *^' 



Pn^.f-''''^^^'''"^' ^V^l,^^^^P°«^d of «ix solid pieces. Base calcareous, cup-shaped ; 

 epizoic on Sponges and Alcyonarians. Pliocene and Recent. 



Fig. 1448. 

 Balanw concamis Bronn. Crag; Sutton, England. .4, Shell. 

 Vi (after Darwin). 



B, Tergum. C, Scutum. 



