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LEPTONIDAE 395
Lasaea cistula Keen Little Box Lepton
Southern half of California to Peru.
Me of an inch in length (one of the smallest of our American clams),
oval-oblong to quadrate, with one end slightly more rounded. Beaks slightly-
nearer the posterior end. Shell very obese to moderately inflated. Color
lis^ht-tan with dark carmine around the dorsal margin area, and commonly
blushed on the sides with light-carmine. Coarse, concentric growth lines,
especially in the adults. Periostracum thin and yellowish tan. Found nestled
together in great numbers attached to seaweed holdfasts and among mussels.
Lasaea subviridis Dall (British Columbia and south) is much more compressed,
smoother, with smaller beaks, but otherwise similar to cistula. Com-
mon.
Genus Pseiidopyth'ina P. Fischer 1884
Shell small and quadrangular. Lateral teeth absent; i cardinal tooth in
each valve.
Fseudopythina rugifera Carpenter Wrinkled Lepton
Alaska to Lower California.
Figure 80a
% to % inch in length, oval-oblong, moderately obese, fairly fragile,
beaks close together and located about the middle of the shell. Shell white,
but in live specimens covered with a thin, light-brown, semi-glossy periostracum
which is feebly and concentrically wrinkled. The ventral edge of the
valves is slightly indented in the middle in some specimens. May be found
attached to crustaceans and the sea mouse, Aphrodita, or be free.
Vseiidopythwa compressa Dall (Alaska to Mexico, the Compressed Lep-
ton) is similar in size and outline, but is considerably compressed (thinner),
smoothly polished in the beak area and with much less periostracum. Common.
Genus My sella Angas 1877
Two cardinal teeth in the right valve, none in the left. Rochefortia
Velain is this genus but a later name by several months.
My sella planulata Stimpson Atlantic Flat Lepton
Nova Scotia to Texas and the West Indies.
% inch in length, oval-oblong in side view, well-compressed, and fairly