252 ENOPLOCHITON. 



Genus XX. ENOPLOCHITON Gray, 1847. 



Enoplochiton GRAY, P. Z. S. 1847, pp. 65, 69, 169. 



Valves exposed, of a uniform dark brown or chocolate color out- 

 side and within ; the lateral areas and head valve irregularly 

 studded with extremely minute eyes. Interior minutely laminated 

 and punctate in a peculiar pattern ; sinus deep, denticulate. Inser- 

 tion-plates of anterior and median valves slit into teeth and sharply 

 pectinated outside. Tail-valve having the mucro posterior and 

 terminal, and inside with a flat ledge of callus in place of the lack- 

 ing insertion-plate. Girdle fleshy, bearing extremely broad and 

 short, blunt, separated striated scales. 



The single species comprised in Enoplochiton resembles the larger 

 Onithochitons in being polished and sculptured with wavy impressed 

 lines (when not eroded) and also in the denticulate sinus, as well as 

 in the structure of all the insertion-plates. It differs from Onitho- 

 chiton in the peculiar texture and color of the valves, the sculpture 

 of the interior and the structure of the girdle. 



The eyes in this genus are extremely minute and oval instead of 

 round. The megalopores and micropores are arranged in vertical 

 lines (pi. 52, figs. 27, 28). The valves resemble those of Mesotomura 

 in most respects, excepting the tail valve, which is that of Onitho- 

 chiton. 



E. NIGER Barnes. PI. 52, figs. 22-29. 



Shell oblong, convex, the valves thick and dark brown outside 

 and within. Surface shining when perfect, but generally eroded 

 and dull. 



The valves are strongly beaked, and generally much eroded ; but 

 when not too much worn the sculpture is as follows : lateral areas 

 marked with undulating longitudinal impressed lines ; central areas 

 having a series of short impressions in front of each diagonal rib, 

 and an impressed V on the ridge of each valve ; anterior valve hav- 

 ing concentric wavy grooves ; posterior valve much depressed, with 

 posterior terminal mucro ; sculptured like the median valves. 



Interior seen under a lens to be sharply, densely laminate in front 

 of the valve callus, punctate on the sutural plates and behind the 

 valve-callus (fig. 25). Sutural and insertion plates of median 

 valves thick, tending forward ; sinus broad, rounded or angular, 

 denticulate; anterior valve having 9 slits, median valves 1 slit; 

 teeth long, deeply, sharply and closely pectinated outside. Posterior 



