230 AXEL A. OLSSON 



Lepton lediformis, new species Plate 36, figure 10 



The shell is small, elongate, equivalve, with the beak near the anterior 

 one-fourth, at which point also the valve is highest and most convex. Hinge: 

 the left valve has a deep socket and a tooth on each side of a wide notch 

 in the tip of the beak which also carries the resilifer; beyond these teeth, the 

 margins of the valves are bevelled; in the right valve, the dorsal margin 

 of the hinge line adjacent to the notch below the beak is sharp and fits 

 into the lateral socket of the opposite valve. The shell wall is thin, sub- 

 translucent and transmits into the interior the images of the fine, hairlike 

 concentrics of the surface; adductor scars are indistinct. Area behind the 

 beaks flat and impressed. Surface smooth and covered with fine, incre- 

 mental growth lines. 



Length 2.5 mm., height 1.6 mm., (a right valve). Length 2.6 mm., 

 height L4 mm. (double valves). 



A small shell with an elongate, Nuculana-Wke shape. 

 Range — Panama. Panama: El Lagartillo. 



Genus LASAEA Brown, 1827 

 Type species by monotypy, Cardium ruhrum Montagu. Recent, Euro- 

 pean seas. 



Shell small, ovate, convex and generally solid, white, red, or brown, 

 smooth except for the minute line of growth. The beaks and umbones are 

 placed a little behind the middle, hence the posterior side is shorter as well 

 as higher, its end well rounded; the anterior side is longer and narrower. 

 The hinge plate is stout, deeply notched under the beak, the cardinal teeth 

 small but with a long, narrow, lateral tooth on the posterior side; the 

 anterior lateral tooth is shorter. The ligament is mostly internal, the resiliiun 

 attached to an elongated groove below the posterior tooth. 



This genus includes a number of small to minute species with convex, 

 solid valves. Where found, they are generally abundant. The color of the 

 shell is usually white, shaded with purple, lilac, or pink. 



The figured example, Lasaea rubra (Montagu), Plate 36, figure 6. 

 Specimen collected by T. L. McGinty, Bbynton Beach, Florida. 



Lasaea species 



Shell small, obliquely rounded or subcircular, solid. The anterior side 

 is somewhat narrowed and a trifle longer, both ends are well rounded. Hinge 

 plate solid, with a deep, wide notch under the beak and bordered by strong 

 teeth on each side. The resilifer occurs as an elongated groove which is 

 placed obliquely under the posterior lateral tooth. The hinge plate and the 

 umbone of the shell are often colored a lilac or coral red. Surface with fine, 

 concentric threads. 



A small Lasaea is known to occur at a few places along the coast of 

 western Ecuador and northern Peru, but because only a few loose valves 

 have been found, its identification with described species has not been 

 attempted. As a rule, species of Lasaea occur in numbers under proper en- 

 vironmental conditions. 



Range — Northwestern Peru and Ecuador. Peru: Negritos; Mancora. 

 Ecuador: Punta Centinella, Santa Elena Peninsula. 



