PAPHIIDA. 161 
elevated, A-shaped, anterior to the pit, bifid and extending to 
the inner margin of the cardinal plate; posterior tooth long, 
elevated, compressed, oblique; posterior cardinal plate widely 
and profoundly channeled. The left valve only is known. 
TREsuS, Gray, 1849. 
Distr.— T. maximus, Midd. (ex, 20.) California. 
Shell oval, oblong, ventricose, gaping posteriorly ; cardinal 
tooth small, lateral teeth very small, connected with the cardinal; 
external marginal ligament separated from the cardinal pit by a 
lamina. 
SCHIZOTHERUS, Conrad, 185%. Very closely allied to Tresus, 
with a deep channel on either side of the cardinal teeth. The 
terminations of the siphons are protected by two solid valves. 
T. Nuttallt, Conrad (cx, 21). 
Fastonia, Gray. 
Distr.—S. rugosa, Gmel. 
Shell thick, oval, radiately ribbed; cardinal tooth of the left 
valve compressed ; anterior lateral tooth nearly perpendicular. 
meRope, H. and A. Ad., 185%. Shell thinner, radiately striated 
or ribbed. HL. Aigyptica, Chemn. (cx, 23). 
Lapiosa, Schmidt, 1832. 
Syn.—Cypricia, Gray. Leucoparia, Mayer. 
Distr.—L. lineata, Say (ex, 24). 
Shell oblong, widely gaping and reflected posteriorly ; posterior 
slope narrow, defined by a carina; lateral teeth distinct, the 
anterior one oblique, near the cartilage-pit ; ligament subexternal, 
marginal, not separated from the cartilage. 
RATA, Gray, 1849. (Lovellia,Ch. Mayer.) Subcordate, ventri 
cose, thin, concentrically plicate, subangulate and gaping behind ; 
cardinal tooth strong; posterior lateral tooth small. JL. canal- 
iculata, Say (cx, 25). 
Famity PAPHIID A. 
Shell subtrigonal, equivalve, close; ligament lodged in an 
internal cardinal pit ; cardinal teeth simple. compressed ; lateral 
teeth rudimentary ; siphons separate, divergent. 
Paputa, Lamarck, 1799. 
Syn.—Eryx, Sw. (not Daud.). 
Distr.—31 sp. West Indies, Mediterranean, Crimea, India, 
New Zealand, Chili; sands at low-water. Fossil; Miocene—. 
P. trigona, Desh. (ex, 26). 
Shell trigonal, thick, compressed, closed; ligament internal, 
in a deep central pit; a minute anterior hinge-tooth, and 1—1 
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