152 CHITON. 



c. Urnbo of tail valve distinctly in front of the middle. 

 d. Riblets of lateral areas rather smooth and fine. 

 e. Dotted or spotted with blue. 



/. Large, black, dots small, magnificus. 



ff. Small ; dots large, murrayi. 



ee. Concentrically lineated with brown or dark, cumingi. 

 eee. Unicolored or blotched. 



f. 17 slits in head and tail valves together, perviridis. 



ff. 22-24 slits in head and tail valves together, quoyi. 



fff. 35 slits in head and tail valves together, subfuscus. 



ffff. 30 slits in head and tail valves together, bowenii. 



dd. Riblets of lateral areas granulose, irregular, or much 



forking. 



e. Lateral areas with 3-4 rows of pustules, granosus. 



ee. Lateral areas with forking or meshing riblets. 



/. Riblets 8-10, fine ; slits in head and tail valves 

 together about 40, virgulatus. 



ff. Riblets coarser, netted ; slits fewer, stokesii. 



cc. Umbo of tail valve about central. 



d. Mucro depressed, slope behind it hardly concave, 



pellisserpentis. 



dd. Slope behind mucro very concave, burmanus. 



bb. Central areas with a smooth band or triangular on ridge of 



each valve. 

 c. Mucro in front of the middle. 



d. Riblets of central areas curved or converging, 



e. Lateral areas sparsely pustulose-1 irate, viridis. 



ee. Lateral areas with interrupted or netted lirse, 



tuberculatus. 



dd. Riblets of central areas parallel or diverging forward. 

 e. Lateral areas and end valves pustulose, granosus. 



ee. Lateral areas and end valves granose-ribbed, 



canaliculatus. 



eee. Lateral areas 1 irate, nigrovirens, perviridis, densiliratus. 

 cc. Mucro about central. 



d. Lateral areas with low, smooth riblets, olivaceus, cereus^ 



affinis. 



dd. Lateral areas with feebly granose riblets, insularis. 



ddd. Lateral areas with granose or nodose ribs. 



e. Lateral areas with 3-4, pleura 25 riblets, discolor. 



