ACANTHOCHITES. 27 



the sides. Posterior valve having the tecjmentum drop-shaped, nar- 

 rower in front, longer than wide; mucro at the posterior fourth. 



Interior deep rose red, paler at the edges of each valve. Slits 

 rather deep and narrow, arranged as usual. Insertion plates of all 

 valves very distinctly rugose outside. Posterior valve normally slit; 

 not noticeably bilobed behind. 



Girdle wide and fleshy in alcoholic specimens, having 18 con- 

 spicuous tufts. 



Gills extending forward two-thirds the length of the foot. 



Length 28, breadth 15 mill, (alcoholic specimen.) 



Panama (McNeill Expedition.) 



Described from an alcoholic specimen which has lost the cuticle 

 and hairs from its girdle leaving a smooth whitish surface pitted at 

 the sutures. The salient specific characters are (1) that the girdle 

 encroaches much at the sutures ; (2) that the substance of the valves 

 is rose-red ; and (3) that the sculpture is altogether peculiar. The 

 insertion-plates are uncommonly rugose outside. It differs from A. 

 hemphilli in the normal 2-slit posterior insertion-plate. 



The pustules (pi. 12, fig. 49 x 60) are mainly rounded or short 

 drop-shaped, and are arranged in regular rows. They become some- 

 what more spaced and less regularly arranged at the sides, and the 

 valve illustrated has suffered erosion toward the beak. The individ- 

 ual pustules (fig. 49) are seen to be decidedly concave. The dorsal 

 area is narrow, elevated and smooth except for growth stride. The 

 insertion and sutural plates are distinctly and sharply striated. 



A. HIRUDINIFORMIS Sowerby. PI. 2, figs. 56, 49. 



Shell oblong, flattened, blackish-green. Valves rounded, granu- 

 lose ; central areas elongated, acuminate behind, smoothish. Girdle 

 very densely pilose, velvety, with 9 concolored bunches of hairs. 



Length 25, breadth 14 mill. (Sowb.*) 



Ancon, Lobos Island and Payta, Peru ; Chatham Island, Galap- 

 agos, under stones at low water. 



Chiton hirudiniformis SOWB., P. Z. S. 1832, p. 59 ; Conch. Illustr. 

 f. 23, 142. REEVE, Conch. Icon., t. 10, f. 54. 



A. STYGMA Rochebrune. PL 8, figs. 31, 32. 



Shell ovate-elliptical, the shell quite wide, pale brown, each valve 

 regularly encircled with a wide concentric black band. Anterior 

 valve rounded ; posterior small, somewhat swollen ; intermediate 

 valves having the central and lateral areas most minutely punctic- 



