+ BOOK OF SPECIES. 
carinated ribs; interstices longitudinally striated, 
and marbled with brown ; inside white. 1... 3. 
Wee 17. 
P. toneicosta. Convex-depressed, reddish 
brown, with from twelve to fifteen sub-carinated 
ribs greatly projecting beyond the margin ; white 
beneath, and the borders acute; vertex obtuse 
and white. 2... 11. 
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ke ae 7 
P. UMBELLA. Large, ovate-depressed, with 
irregular decussated striz, and narrow longitu- 
dinal grooves ; margin crenated, white or yellow- 
ish streaked, and sprinkled with dots of pale 
vermilion or rose-colour in various ways. Up to 
Deena. 7 Wite/one4. 
P. cocHLEAR. Ovate-oblong depressed, lon- 
gitudinally ribbed and striated, one end con- 
