314 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
been crowded together from the ends. The slits are practically as in 
Mopalia, being normally (or at least originally) 8 in the head valve; but 
the number is frequently increased by the splitting of some teeth. The 
mantle-edge is produced in front and fringed with long, fleshy, finger-like 
processes. The longer hairs of the girdle are extremely peculiar, being 
covered with imbricating scales like a snake skin, on a corneous core. 
Nothing of the sort has been found in any other group of Chitons. (Tryon 
and Pilsbry, Manual of Conchology .) 
Type. Placiphorella velata Carpenter. Carpenter’s MS name. 
Distribution. California, Lower California, Japan, Bering Sea, Peru. 
Placiphorella pacifica Berry, 1919 
Lorquinia, January 1919, 6. 
Shell obovate, depressed. Anterior valve with 12-14 low, radiating 
ribs. Central areas of median valves nearly smooth; lateral areas raised, 
ornamented with 2 low, weakly nodulose ribs. Tail valve small, with sub¬ 
terminal mucro. Head valve with 16 slits, median valves with 1-1 slits, 
tail valve slitless. Girdle narrow behind; expanding into a broad lobe in 
front; covered dorsally by minute, microscopic spinelets, and occasional 
slender spinose setae and tufts of spines. (Berry.) 
Type in Berry Collection. Type locality, Station 4245, Kasa-an Bay, 
Alaska, in 95-98 fathoms. 
Range. Known only from type locality. 
Placiphorella borealis Pilsbry, 1892 
Tryon and Pilsbry, Manual of Conchology, 14:309; PI. 66, figs. 14-17. 
Shell similar in general characters to P. velata. Brown at the sides, 
light along the middle. Surface dull, showing growth-lines. Valves not 
beaked, having a slight forward bend in the middle at the sinus, but not 
“false beaked” there as P. velata is. Lateral areas more strongly two- 
ribbed. Anterior valve sculptured with numerous very low, wide, radiating 
riblets. Posterior valve having the mucro near the posterior margin, de¬ 
pressed, the slope in front of it rising, convex rather than concave; 
posterior margin waved inward. Interior light blue-green. Sutural plates 
separated in all the valves by an angular, spongy sinus. Anterior valve 
having 11 slits, the teeth being peculiarly curved outward at its edges. 
Posterior valve much less callous inside than that of P. velata, the inser¬ 
tion-plate uneven, roughened, but having a single, well-developed slit on 
each side; the median tail-notch deep and wide. Eaves very spongy. Girdle 
unknown to me. Breadth of anterior valve 16, length of front slope, 
[916] 
