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 com- 

 pressed, 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 



Figure 80a 



Alaska to Lower California. 



% 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 periostra- 

 cum 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. Com- 

 mon. 



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 



