PANAMIC-PACIFIC PELECYPODA 391 



The shell is large or small, elongate-ovate, compressed to slightly 

 convex, the posterior side equal or but a little shorter than the anterior, 

 weakly flexed or not at all, sloping and generally obliquely subtruncated or 

 pointed at the end, the beaks usually submedian. The posterior-dorsal 

 slope has usually a narrow rostral area, more strongly sculptured than the 

 surface below it and setoff by a low angle. Surface smooth and glossy in 

 some species but more often with fine, evenly spaced, incised concentric lines 

 forming narrow ribbons. Hinge with both cardinal and lateral teeth, the 

 anterior lateral placed close to the cardinal; right posterior cardinal and left 

 anterior posterior teeth bifid. Pallial sinus is deep, rounded at the end, or 

 extended across to touch or connect with the anterior adductor scar, its 

 lower limb coalescent with the pallial line below. Ventral margin smooth, 

 rarely with irregular crenulations. 



In most works, Eurytellina is classed as a subgenus of Tellina, but the 

 group is entitled to a higher rank. It includes our most common tellinids. 



Two subgenera. 



I. Posterior area above the umbonal angle sculptured similar to that of 

 the main disk. 



Subgenus Eurytellina, s.s. 



II. Posterior area sculptured with squamose foliations or with fine, plate- 

 like scales. 



Subgenus Phyllodella 



General key to Panamic species of Eurytellina, s.s. 



I. Shell generally solid in texture and of a white color only. 



A. The pallial sinus is large and deep, so that it covers most of the interior 

 of valve; Its upper limb attached lightly to the anterior adductor scar 

 with a small area between the adductor scar and the pallial line open. 



1. Rather solid, elongated valves with nearly median beaks and a smooth, 

 glossy surface. The posterior flexure is weak. 



E. laceridens 



2. Shell higher with the beak placed a little behind the middle line, the 

 posterior end more strongly flexed. Surface covered with narrow, con- 

 centric ribbons. 



E. hertleini 



B. The pallial sinus is shorter, its end partly rounded, and set well apart 

 or not in contact with the anterior adductor scar; the lower limb of the 

 sinus confluent with the pallial line for about four-fifths of its length. 



3. Dorsal margin of the left valve widely expanded and sculptured with 

 coarse, widely spaced, transverse wrinkles. Concentric ribbons of the 

 surface sculpture rather large and coarse (about .75 mm. wide each). 



E. laplata 



4. Dorsal margin of the left valve not so widely expanded, sculptured 

 with finer longitudinal threads. 



E. eburnea 

 II. Texture of shell more varied, thin or thick, the color white, red or pink 

 in the same species. 



C. Pallial sinus large and deep, its upper limb extending across to connect 

 directly with the anterior adductor scar, no triangular space below, the 

 lower limb of sinus and the pallial line continuous. 



5. Shell small or of medium size, usually colored red or pink. 



E. rubescens 



