PANAMIC-PACIFIC PELECYPODA 383 



Length 22.8 mm., height 15.9 mm., diameter 4 mm. (left valve), Guani- 

 co, Panama. Paratypes, ANSP 218943, 218944. 



Differs from M. crystaUina by its heavier, more stubby valves, stronger 

 and coarser sculpture, its curved dorsal margins (the posterior one is deeply 

 concave) and also by the deeper ray or sulcus which extends in front of the 

 rostral ridge. 



Range — Panama to Ecuador. Panama: Bucaro; Guanico. Ecuador: 

 Santa Elena; Manglaralto; San Francisco (Galeras Peninsula). 



Merisca margarita, new species Plate 70, figures 5, 5a 



Shell elongate to ovate-trigonal, small or of medium size, relatively thin, 

 white. The valves are slightly unequal in shape, both are moderately convex, 

 the left uniformly so over the whole disk, the right valve, convex along the 

 umbonal slope and slightly flattened or impressed in the posterior-middle 

 zone. The posterior flexure is of moderate size, ending in a short snout 

 turned towards the right. Surface is covered with fine, close-set, concentric 

 lamellae developed evenly over the whole disk (these usually run about 3/4 

 to 4 in the space of a millimeter). Hinge normal, the posterior lateral tooth 

 well removed from the cardinals, the anterior one spaced a little closer. 

 Pallial sinus is large, its upper limb, high and angular in the middle and 

 reaching to the anterior adductor scar which it barely touches at its lower 

 edge, the lower limb confluent with the pallial line for its whole length. 



Length 19.8 mm., height 15 mm., diameter of a right valve 3 mm. 



A distinctive species, recognized by its finer sculpture, more elongated 

 shape, and nearly equal convexity of both valves. Its Atlantic analogue is 

 M. aequistriata (Say). Holotype, ANSP 218945. 



Range — Panama, Panama: Puerto Chame. San Miquel, Rey Island, 

 Pearl Islands, 



Genus LTKATELLINA, new genus 



Type species, Tellina lyra Hanley. 



Valves elliptical in shape, white or glassy, equal, depressed, or slightly 

 convex; the beaks median, prosogyrate, the posterior side rounded, unflexed, 

 but with a narrow, strongly sculptured rostral area. The surface is sculptured 

 with strong, concentric ridges between wide, flat interspaces. The ligament 

 is external but lies partly immersed in the hinge plate, the margin of the shell 

 rising above the ligament scar. The hinge is normal and strong; in the right 

 valve, there is a single, bifid, cardinal tooth, its posterior arm large, inclined, 

 bordered on the sides by sockets; there is a lateral socket on each side, the 

 anterior one plr.oed a little closer to the cardinal teeth, the lower rim of each 

 socket is enlarged to form a tooth; the left valve has a single, small, narrow, 

 bifid, cardinal tooth bordered on the sides by sockets, the lateral teeth are 

 merely slight enlargements of the hinge margin. There is a small, sunken 

 lunule, larger in the left valve and not set apart by a line. The escutcheon is 

 narrow and deep, the margin of the valve arising above it as a narrow wing. 



The type species (Tellina lyra) was referred by Dall and some later 

 authors to Macaliopsis Cossmann, 1886 (type species, Tellina barrandei 

 Deshayes, an Eocene shell from the Paris Basin) but the resemblance of the 



