946 PELECYPODA. [Eulamellibrunchia. 



Shell -substance cellulo - crystalline, with an inconspicuous epi- 

 dermis ; valves slightly inequal, free, rounded in front, more or less 

 rostrate, oblique and gaping behind, compressed, usually with smooth 

 margins, low beaks, and variable (chiefly concentric) sculpture ; 

 anterior adductor-scar larger, frequently irregular ; pedal distinct ; 

 resilium embraced in the ligament, subexternal ; area narrow, small, 

 covered with a dark epidermis, or frequently obsolete ; hinge-plate 

 narrow, anterior laterals approximate, posterior more distant from 

 the cardinals, when present ; cardinal teeth small ; pallial sinus deep, 

 discrepant in the opposite valves. 



Jura to Recent. 



KEY TO GENERA. 



A. Each valve with 2 cardinal teeth and 2 laterals, the latter most 



distinct in the right valve . . . . . . . . TELLINA. 



B. Both valves with 2 cardinal teeth, left valve very often with the 



posterior cardinal obsolete ; no lateral teeth . . . . MACOMA 



Genus 1. TELLINA (Linne), Lamarck, 1799. 



Tellinu, L., Syst. Nat., ed. 10, 1758, 674 ; Lamarck, Prodrome, 1799, 84. 

 Type : Tettina viri/ata, L. 



Animal ovate, compressed, mantle entirely open in front, its margin 

 fimbriated ; siphons long, separate throughout, usually nearly equal, 

 their orifices plain, or very indistinctly toothed. Foot large, tri- 

 angular, compressed, apiculate. Labial palpi large, lanceolate. 



Shell subequivalve, rather compressed, suborbicular or trans- 

 versely elongated, obliquely flexed behind ; beaks subcentral ; hinge 

 with 2 cardinals and generally 2 laterals in each valve, 1 lateral anterior 

 and 1 posterior, the laterals most distinct in the right valve ; pallial 

 sinus wide and deep ; ligament external, prominent. 



Distribution. World-wide ; over 400 species are known. 



Fossil in the Cretaceous and Tertiary. 



The molluscs of this genus live in sand or sandy mud, buried 

 beneath the surface ; the majority at low- water mark or in consider- 

 able depth. A few species have a range from the coralline zone to 

 about 450 fathoms. 



KEY TO SUBGENERA. 



A. With 2 lateral lamina? in each valve, those in the left valve 



always less strong . . . . . . . . . . TELLINA, s. str. 



B. With 2 lateral laminse in the right valve, one or both of those 



of the left valve absent or obsolete ; sinus free . . ARCOPAGIA. 



C. Hinge with a strong right anterior lateral, closely adjacent 



to the cardinals, the left laterals absent, the posterior 



right lateral obsolete, with internal thickened radii . . ANOULUS. 



Subgen. 1. TELLINA, s. str. 



Type : T. virgata, L. Angulus, Megerle, 1811. Tettinella, " Gray," Mo'rch, 

 1852. Eutellina, Fischer, 1887. 



Valves sculptured externally, the concentric sculpture stronger ; 

 somewhat compressed, ovate-trigonal, subequivalve, with a more or 



