652 DESCRIPTION OF PLATES, 18, 19. 



PLATE 18. 



Genus — Chthamalus. 



Fig. 1 a, Chthamalus stellatus, shell, var. a (communis). 

 1 b, ,, ,, ,, ,, e (depressus). 



1 c, ,, „ ,, ,, c (communis). 



1 d, „ „ „ „ d (fragilis). 



1 e, „ ,, scutum and tergum, viewed inside, var. c, 



British. 

 If, ,, ,, scutum and tergum, viewed inside, var. a, 



Madeira. 

 1 g, „ „ scutum and tergum, viewed inside, var. e, 



Mediterranean. 

 1 h, „ „ scutum and tergum, viewed inside, var. c 



and e, St. Jago, Cape de Verde Arch. 

 2, Chthamalus antennatus, shell. 



3 a, Chthamalus dentatus, shell ; 3 b, var. shell, attached to a 



ship's bottom ; 3 c, tergum, viewed from within. 



4 a, Chthamalus cirratus, scutum, viewed on inside ; 4 b, tergum, 



viewed on inside. 



5 a, Chthamalus Hembeli, shell, old specimen. 



5 b, Chthamalus Hembeli, younger shell ; c, carino-lateral com- 

 partment ; a', ala ; d, radius ; e, carina ; a', the two alse. 



5 c, Chthamalus Hembeli, scutum, external view of; bd, tergum, 



external view of, ; e, two of the crests, to which the tergal 

 depressor muscles are attached, much enlarged and viewed 

 from vertically beneath, showing the lateral denticuli or 

 sub-crests. 



6 a, Chthamalus fissus, shell ; 6 b, scutum and tergum, separated, 



internal views of. 



PLATE 19. 



Genera — Chthamalus, Cham^sipho, and Pachylasma. 



Fig. 1 a, Chthamalus intertextus, shell; 1 b, scutum and tergum, calci- 

 fied together, with the suture obliterated in the upper part, 

 internal view of. 

 2a, Chthamalus scahrosus, shell; 2b, scutum, internal view of; 

 2 c, tergum, internal view of, p, plate forming one side 

 of the cavity in which the depressor muscle is attached ; 

 2 d, tergum, as seen from almost vertically beneath ; 

 p, pit for the depressor muscle ; q, special pit for the lateral, 

 properly scutal depressor muscle; r, articular furrow. 



3 a, Chamsesipho columna, shell ; a, rostrum ; b, lateral compart- 



ment, probably formed by fusion of the rostro-lateral and 

 lateral compartments ; e, carina ; 3 b, 3 c, scutum and 

 tergum, internal views of. 



4 a, Chamrcsipho scutelliformis, shell much enlarged, seen from 



above ; a, rostrum, separated by imperfect sutures from 

 the (b) lateral compartments, which are formed probably 



