308 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Mopalia imporcata Carpenter, 1864 
Supplementary Report, British Association for the Advancement of Science, 648. 
Tryon and Pilsbry, Manual of Conchology, 14:301; PI. 62, fig. 98. 
Pale: central areas ribbed: post, valve slightly notched. Indications of 
sutural pores in these two species, if confirmed, will require a new genus. 
(Carpenter.) 
Shell small, oblong, strongly elevated and acutely carinated, the side- 
slopes straight. Buff-white, slightly stained with rust-brown. The median 
valves are acute at the umbo, but there is no projecting beak; lateral areas 
bounded by a strongly elevated, narrow, crenulated, diagonal rib, and 
having a wider rib at the sutural margin, also crenulated, thus denticulating 
the suture; the space between the two lateral ribs being finely corrugated- 
granose. Central areas sculptured with strong, curved, longitudinal ribs, 
which converge forward somewhat, toward the median keel; the intervals 
between these ribs being closely and finely latticed across by threads radi¬ 
ating from the beaks. Anterior valve having 8 strong, narrow, raised ribs, 
with one wider rib at each sutural edge. Posterior valve depressed, the 
mucro situated at the posterior end. Interior white; sinus very small and 
shallow. Anterior valve having 8, median 1 slit; teeth but little thickened 
along the slits. Posterior valve having a rather wide, moderately deep, 
rounded, tail sinus, and a single slit on each side. Girdle leathery, dusty, 
with a hair-pore at each suture, and some scattered or alternating hairs. 
Length, 10; breadth, 6 mm.; divergence, 95°. (Tryon and Pilsbry, Man¬ 
ual of Conchology .) 
Type in United States National Museum. Type locality, Puget Sound. 
Range. Forrester Island, Alaska, to San Pedro, California. 
Mopalia imporcata lionotus Pilsbry, 1918 
Nautilus, 31:126. 
This chiton agrees closely with M. imporcata except that there is a 
narrow, smooth jugal tract. The lateral areas are granose between the 
coarsely tubercular diagonal and sutural ribs. The anterior valve has 10 
ribs. Posterior valve is depressed behind the mucro, which is at the 
posterior fourth. Interior light Niagara-green, darker posteriorly on each 
valve. The girdle bears branching processes, often like the branches of 
spines on a cactus. These are scattered, sometimes sutural. Length, 15.5; 
width, 9 mm.; divergence, 95°. (Pilsbry.) 
Type in Philadelphia Academy of Natural Sciences. Type locality, 
White Point, California. 
Range. San Pedro and White Point, California. 
[910] 
