CLASS GASTROPODA 
281 
Squamae hae in series oblique decurrentes ordinate. Long., 0.23 decim. 
(Middendorff.) 
Shell oval, elevated, with angular dorsal ridge, and straight sideslopes. 
Varying in color from orange-red to claret-red, or even dark red-brown, 
and either unicolored or speckled and blotched with white. The lateral 
areas are elevated, and sculptured with radiating rows of elevated pus¬ 
tules standing upon a smooth, almost flat ground; the pustules of the 
sutural row often irregular. Central areas having acute, narrow, parallel, 
raised riblets, the intervals between them regularly latticed across, except 
at the dorsal ridge, where the riblets have a tendency to diverge, and cross- 
hatching is obsolete. End valves radially pustulose. Mucro central, low, 
flat, and inconspicuous. Interior white or blue-white, the median valves 
when detached showing broad red-brown rays posteriorly, the end valves 
with crescents of the same color. Sutural plates low, sinus flat, angular, 
finely toothed. Anterior valve having 10-11, central valve 1, posterior 
valve 10 slits; teeth rather short and obtuse, and usually distinctly rough¬ 
ened; eaves rather wide. Girdle firm, compactly covered with regular, 
solid, oval, shining scales, which are usually smooth but frequently are 
superficially or obsoletely striated. Length, 35; breadth, 21 mm. (Tryon 
and Pilsbry, Manual of Conchology.) 
Type in Academy, St. Petersburg. Type locality, California. 
Range. Sitka, Alaska, to San Pedro, California. 
Described as Chiton mertensii. 
Ischnochiton cooperi (Carpenter) Pilsbry, 1892 
Tryon and Pilsbry, Manual of Conchology, 14:127; PI. 26, figs. 27-30. 
Shell oval and elevated, with angular dorsal ridge and straight side- 
slopes. Sculpture like I. mertensii. Color olivaceous, or dull earthy brown, 
indistinctly clouded more or less with light blue, especially upon the side 
areas. The lateral areas are raised, and bear irregular rows of rounded 
pustules, the young having four rows, the adult 6 to 8. A strong lens 
reveals a fine, subobsolete granulation of the nearly flat surface between 
the pustules. The central areas have a fine but distinct and even radial 
striation, over which run acute narrow raised threads parallel to the dorsal 
ridge; upon the ridge these threads are seen to be more or less diverging, 
especially upon the second valve. The end valves are radially ridged, the 
ridges bearing elongated pustules, or showing scars where such pustules 
have been. Mucro low, flat. Interior bluish, the valves marked under 
their umbones with dark teeth roughened but rather sharp; eaves wide, 
dark, minutely punctulate, but solid, not spongy. Girdle compactly covered 
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