CLASS GASTROPODA 
313 
reaching the mucro, the anterior sinus also narrow and acute, the sutural 
laminae broad; jugal and pleural areas of the intermediate valves not 
separated, the sculpture of oblique reticulation with emphatically punctate 
interstices; lateral areas similarly sculptured, bounded on each side by a 
slender rib, internally whitish with a narrow notch-like sinus. Length, 12; 
width, 6; height, 4 mm. (Dali.) 
Type in the United States National Museum, No. 208703. Type 
locality, Granite Cove, Port Althorp, Alaska. 
Range. Granite Cove, Port Althorp, Alaska, to Puget Sound. 
Mopalia celetoides Dali, 1919 
Proceedings of the United States National Museum , 55:514. 
Chiton with sculpture almost exactly like No. 218770, except that the 
latter has more globular nodules on the lateral ribs and the pleural tracts 
are less coarsely and evenly reticulated. In the present species the anterior 
valve has 10 radial ribs with wider channeled interspaces minutely reticu¬ 
lated; the posterior valve, however, entirely different, having a posterior 
mucro with a small rounded sinus below it, and not ribs, the surface being 
taken up by the central area which has very straight axial threads minutely 
annulated, with much finer and closer transverse threads visible in the 
interspaces; gill-rows extending forward as far as the fourth valve; 
posterior valve with 2 slits, anterior with 8, intermediate with one at each 
end; intermediate valves with the lateral areas bounded by two strong 
ribs, the posterior wider, denticulated; jugum minute with a small smooth 
mucro, the back slightly keeled in front of it, the pleural tracts with about 
11 strong axial threads. Length, 12; width, 5.5; height, 2.5 mm. (Dali.) 
Type in United States National Museum, No. 218771. Type locality, 
Forrester Island, Alaska. 
Range. Known only from the type locality. 
Genus PLACIPHORELLA Carpenter, 1878 
Valves very broad and short, the middle ones much broader than those 
toward the ends; head valve narrowly crescentic, tail valve still smaller, 
with posterior mucro. Sinus small; insertion-plates short and thick, the 
teeth lobed or rugose. Slits 8 or more in the anterior, 1 in the median, 2 
in the posterior valve, which has also a shallow, posterior sinus. Eaves 
spongy. Girdle widest, often very wide, in front, bearing sparsely scat¬ 
tered, scaled hairs. 
This genus differs from Mopalia in the rotund contour of the valves 
taken together, and their extreme shortness individually, as if the shell had 
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