ACANTHOPLEURA. 227 



sinus not toothed, the sutural plates connected across it ; girdle 

 thick, densely beset with calcareous spinelets. Type Ch. granulatus 

 Gmel. 



This subgenus or section differs from Acanthopleura and Mesoto- 

 mura in the shorter, blunt tail insertion -plate, and the proportionate 

 breadth of the outer and inner layers of the median valves. It 

 differs from Amphitomura in having numerous equally developed 

 slits in the insertion-plate of the tail valve. 



A. GRANULATA Gmel. PI. 50. 



Shell oblong, moderately elevated or roundly arched. Surface 

 almost always eroded, dull, ashy or cinereous, generally with a 

 patch of dead-leaf brown on the ridge of each valve ; when not 

 eroded, it is tawny-brown or black-brown, with a pair of diverging 

 whitish, buff or pinkish stripes. 



The valves are beaked, solid and thick, with somewhat raised but 

 ill-defined lateral areas. When not eroded, the lateral areas and 

 pleura are closely granulated all over, and the end valves likewise ; 

 but this sculpture is generally preserved only at the lateral extrem- 

 ities and the protected anterior margin of each valve. The mucro 

 is swollen and posterior. 



Interior sea-green, often varying toward lead-blue, or on the 

 sutural-plates fading to nearly white ; each median valve having a 

 black or purple- black tract between the sinus and the summit of the 

 callus, fyis tract being square or 2-branched at the ends. Anterior 

 valve having normally 8-10, central 1 (rarely 2), posterior valve 9, 

 (occasionally 7-14) slits; teeth long and very deeply pectinated 

 outside; teeth of tail-valve short and obtuse, directed forward, very 

 deeply pectinated outside and on the edge. Sinus slightly concave, or 

 convex and notched at the sides, not denticulate. 



Girdle thick and fleshy, densely covered with short, unequal spine- 

 lets (pi. 50, figs. 40, 41, x 13) which are short, calcareous, and either 

 black or white ; the black spines (fig. 41) being frequently longer 

 than the white, and straight or nearly so ; the white spines (fig. 40) 

 are short, very unequal and shaped like the shell of Cadulus. 



Bermuda; Bahamas; Charlotte Harbor, Vaccas Key, etc., west 

 Florida ; entire West Indies, southward to Trinidad and the Spanish 

 Main. 



Chiton magellanicus GMELIN, Syst. Nat. xiii, no. 12, p. 3204. 

 ( Chemn. viii, p. 279, pi. 95, f. 797, 798, Chiton magellanicus'). 



