PANAMIC-PACIFIC PELECYPODA 4U 



subrhomboidal, the left valve a little larger than the right, more convex 

 over the umbonal slope, depressed behind the posterior keel. Surface white 

 and irregularly marked with coarse lines of growth. 



A left valve from Paita measures: length 84 mm., height 73 mm., 

 diameter 20 mm. 



This species, although plentiful along parts of the coasts of Peru and 

 Ecuador, has remained little known and poorly represented in most collec- 

 tions. It is similar to the northern F. biangidata (Carpenter) in its flaring 

 and less steeply sloping posterior area and much narrower, weaker hinge. 

 It is also closely related to F. magnoUana (Dall), a Miocene and Pliocene 

 species from Florida and the Carolinas, as well as to F. biplicata (Conrad) 

 from the Miocene of Maryland. 



Range — Panama to northern Peru; also the Galapagos Islands. Panama: 

 Guanico; El Lagartillo; Las Tablas. Panama Canal Zone: Venado Beach; 

 Palo Seco. Ecuador: Sua; Charapota; Santa Elena. Peru: Boca Pan; Man- 

 cora; Paita; Bayovar. 



Genus PSA3DI0TRETA Dall. 1900 



Type species by original designation, Tellina aurora Hanley. 



The valves are elongately ovate to trigonal, the posterior side shorter 

 than the anterior, its dorsal margin descending to fo'"m a narrower and 

 sometimes slightly expanded or winged posterior area. The posterior flexure 

 may be weak or strong. Except for the flexure, the valves are generally 

 similar in shape and degree of inflation, the greatest zone of convexity 

 lying diagonally along the anterior-umbonal slope. The adductor scars are 

 unequal in size, the posterior one long and narrow. The pallial sinus is 

 deep and rounded at the end, its lower limb coalescent in part with the 

 pallial line. The surface is smooth except for lines of growth and occasionally 

 with still finer, radial striae. The ligament is external, its scar relatively 

 short and formed by an excavated or inset pit in the hinge plate, crowded 

 against the cardinal tooth which may be partly obliterated by it. 



Psammotreta Dall was based on Macoma aurora Hanley, a species 

 with elongate-quadrate valves, the posterior side with a weak flexure; its 

 ligamental scar is short and subtriangular in shape and so deeply immersed 

 in the hinge plate that the adjacent cardinal tooth is partly obliterated by 

 it. The larger and more trigonal species such as P. dombei have similar 

 hinge and ligament features but the valves are more strongly flexed, so 

 that the posterior-dorsal area may be slightly winged; such species have 

 often been referred to Apoly metis (Florimetis) but the posterior area is 

 never so broadly winged or the posterior flexure so sharply folded as in the 

 typical species of that genus. Psammotreta is allied to Florimetis as shown 

 by its unequal adductor scars and immersed ligament. 



Fsammotreta aurora (Hanley) Plate 74, figures 6, 6a 



Tellina aurora Hanley, 1844, Proc. Zool. Soc. London, p. 147 Panama.— Hanley, 1846, 

 Thes. Conch., vol. 1, Tellina, p. 301. No. 153, pi. 58, fig. 76. 



Macoma {Psammacoma) aurora (Hanley), Salisbury, 1934. Proc. Malacol. Soc. London, 

 vol. 21, pt. 2, p. 91, pi. 11, fig. 4 (figure of lectotype). 



Macoma {Psammotreta) aurora (Hanley), Hertlein and Strong, 1949, Zoologica, vol. 

 34, pt. 2, No. 9, p. 92. 



