358 AXEL A. OLSSON 



rather short, extending to the middle, complete and rounded at the end. 



The nymphal plate is distinct but not as high or prominent as in panamensis. 



Length 52 mm., height 27.3 mm., diameter 14.3 mm. Holotype, ANSP. 



In shape, this species resembles G. regularis but is more slender, the 

 posterior side narrower and more flexed, and the coloration is different. 

 Faint, radial, divaricating lines may be seen on the posterior-dorsal area 

 under a lens. 



This species is named for Mrs. Helen L. Beil, a capable and enthusi- 

 astic collector of Panama shells. 



Range — Panama. Panama: Pearl Islands, (Coll. Lee Beil). 



I^mily SEMELIDAE 



Shell small or large, heavy or thin, orbicular to elliptical in shape, the 

 valves convex or depressed. The ligament is mostly internal, the resilium 

 attached to an obHque groove in the hinge plate or to a bulging spoonlike 

 chondrophore, the tensilium small, narrow and placed above a wide, flat- 

 tened nymph. Hinge teeth variable in strength, the cardinals usually small 

 or obsolete, the lateral teeth absent or strong. The pallial sinus is large, 

 rounded at the end. Ventral margins smooth. 



Members of this family resemble the Tellinidae but are distinguished 

 by the large internal ligament attached to an obliquely grooved resilifer. 

 Five genera of the family occur in the Panamic-Pacific region. In key 

 form, these genera may be distinguished as follows: 



1. Pallial sinus large, entire, rounded at the end, free, its lower limb not 

 united with the pallial line below. 



L Shell large or of medium size, usually rounded or elliptical in shape. 

 Sculpture varied, smooth, or with radial and concentric elements or 

 a combination of both. 



Genus Semele 



2. Shell small, subovate, nuculiform, the anterior side longer than the 

 posterior, rounded at the end. Cardinal teeth stout. Surface marked 

 with concentric riblets only. 



Genus Semelina 

 II. Pallial sinus with its lower limb widely confluent with the pallial line. 



A. Hinge with strong lateral teeth. 



3. Shell free, or more often a nestler, hence distorted in shape. Sculpture 

 concentric, often lamellose. Hinge strong. 



Genus Cumingia 



4. Shell small, regular in shape, trigonal or quadrate. Hinge weak. Sur- 

 face smooth or with fine concentrics. 



Genus Abra 



B. Hinge without lateral teeth. Resilifer grooved, not projecting into the 

 hinge cavity. 



5. Shell elongately trigonal in shape, usually thin. 



Genus Leptomya 



Genus SEMELE Schumacher, 1817 

 (Amphidesma Lamarck, 1818) 

 Type species by monotypy, Tellina reticulata Spengler (^zTellina pro- 

 fkua Pulteney). Recent, Florida, West Indies, and the Caribbean. 



