258 AXEL A. OLSSON 



beaks, anterior in position, the posterior side usually the longer. The hinge 

 is always well developed with radial cardinal teeth under the beaks, usually 

 three in each valve, simple or bifid; in Mercenaria, there is a coarsely rugose, 

 supplementary, posterior cardinal tooth in each valve, the asperities of 

 which form the interlocking surface; in Tivela, the cardinal teeth are 

 multiple or divided into smaller units. A heart-shaped lunule and an escut- 

 cheon are generally present or one or both may be wanting. The ligament is 

 always external, situated behind the beaks, the resilium portion attached 

 to a large scar above or along the upper face of a nymphal ridge. The 

 pallial sinus is always present, sometimes quite small as in Chione, s.s. 

 Surface smooth and plain or marked with a strong sculpture of radial ribs 

 and concentric folds or lamellae, often a combination of both. Color of 

 surface varies from drab white to highly tinted, often with complicated 

 markings. Periostracum thin or coarse. 



The Veneridae is an important family of mollusks in the Panamic- 

 Pacific region with many genera and species, some of great beauty both in 

 coloration and sculpture. Dall characterized this family as being the most 

 beautiful, genetically the most highly evolved, as well as most profilic in 

 species of all bivalves in the Recent fauna. Several species are much sought 

 for as important items of sea food. Several classifications of the Veneridae 

 have been proposed; in this work, the family is divided into six groups or 

 subfamilies as follows: 



Panamic-Pacific subfamilies of the Veneridae 



I. Shell suhcircvlar to suborbicidar, slightly to strongly convex, the sur- 

 face marked with concentric sculpture only, the color white. Hinge 

 plate relatively long and high, bearing three cardinal teeth in each 

 valve of which one or more may be double or bifid. The anterior lateral 

 tooth if present (as in Dosinia) is small and is placed close to the 

 cardinal tooth. Ligament scar large and occupies much of the hinge 

 plate. Ventral margins smooth. 



Subfamily Dosiniinae 



II. Shell circular to orbicular, thin, convex and sculptured with large,*^^^^, 

 concentric undulations which are so strongly impressed that they show 

 well in the interior. Ventral margins are smooth. 



Subfamily Clementiinae 



III. Shell with nearly equal sides and submedian beaks. Hinge with a large, 

 anterior lateral tooth in the left valve and placed apart from the 

 cardinals, its complementary socket in the right valve. The cardinal 

 teeth are normally three in each valve, but in Tivela some of them are 

 divided or supplemented by auxiliaries. Ventral margins smooth. Sur- 

 face usually highly colored. 



Subfamily Meretricinae 



IV. Beaks strongly anterior in position. Hinge with three cardinal teeth in 

 each valve, no auxiliaries, and a large, anterior lateral tooth in the left 

 valve and its socket in the right. Surface smooth or marked with con- 

 centrics. Ventral margins smooth. 



Subfamily Pitarinae 



V. Shell subcordate to subtrigonal, generally solid. Hinge plate stout, 

 usually bearing three cardinal teeth in each valve, sometimes supple- 

 mented by a small or rudimentary, anterior lateral tooth. A lunule and 



