280 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Anterior valve with 35^5 low, occasionally bifurcating, radiating ribs, 
separated by shallow distinct grooves and bearing a variable number (nor¬ 
mally 8 to 10) of small, well-separated, distinct, rounded pustules. Median 
valves: lateral areas distinctly raised, sculptured like the anterior valve, 
but the 5 to 7 ribs relatively wider and more flattened, the defining grooves 
sometimes, but not always, sharply chiseled; central areas on each side 
sharply sculptured with 20-25 narrow, faintly beaded, longitudinal ridges, 
their interstices traversed by low, rather irregular cross-ridges, becoming 
nearly or quite obsolete at the jugum. Posterior valve with mucro sculp¬ 
tured like the anterior valve, but the 28-30 ribs rather less distinct and the 
grooves less conspicuous; region in front sculptured like the central areas 
of the intermediate valves. Interior of central valves thickened across the 
middle. Teeth with a distinct fossa separating them at base from body 
of shell, their edges roughened, those of the posterior valve almost cremate. 
Anterior valve with 11, second valve with 2-1, third to seventh valves with 
1-1, posterior valve with 12 slits. Girdle wide, regular; covered dorsally 
with a closely imbricating armature of large, smooth or barely striated, 
convex scales, each normally bearing a short, striated, nipple-shaped pro¬ 
cess projecting upward from the dorsal end. Color of outer surface of 
shell, reddish-brown of varying intensity in different specimens, sometimes 
nearly black; girdle lighter. Interior of shell, light salmon. Maximum 
length of the type and largest specimen, 29.5 mm.; width, 16 mm. 
(Berry.) 
Type in Berry Collection, No. 3700. Type locality, Forrester Island, 
Alaska, 15-20 fathoms. 
Range. Known only from type locality. 
Ischnochiton mertensii Middendorff 
Bulletin, Imperial Academy of Sciences, St. Petersburg, 6:118. Tryon and Pilsbry, 
Manual of Conchology , 14:125; PI. 26, figs. 20-26. 
Chiton testa externa ovali elevata opaca, aspera, fusco-cinerea; .... 
valva valvae ultimae area postica, valvarum dcnique intermediarum areis 
lateralibus radiatim expresse granulosocabris.Valvarum interme- 
diatum areis centrilibus et valvae ultimae area antica longitudinaliter es- 
culpte-costatis, costis medianis postica versus dichotomia; costarum inter- 
stitia lamellulis erectis transversis in loculamenta dissepta.Valva 
antica dentibus marginalibus 13 et radiis granulosocabris 26.Valva 
ultima margine postico convexo dentibus 13 et radiis granulosocabris 20. 
. . . . Valvarum intermediarum radiis granulosocabris quinque. Pallium 
marginale epidermide fuscocinerea, squamis aspera, obtectum. 
[882] 
