414 . AXEL A. OLSSON 



The shell small or of medium size, relatively thin, white, under a thin, 

 deciduous buff periostracum, inflated in the anterior half, which has a 

 broadly rounded outline, tapering to the truncated posterior end which is 

 bent a little towards the right. The small beaks are behind the middle. 

 The right valve has an obtuse, post-basal ridge, and is broadly flattened 

 or weakly concave in front of it. Pallial sinus large, high, extending deep 

 into the valve cavity but confluent with the pallial line below only for a 

 short distance near its opening. Surface plainly sculptured with growth 

 lines only. 



Length 58.5 mm., height 40.5 mm., diameter 25 mm. (Type ANSP 

 116052 La Union, Gulf of Fonseca, San Salvador. 



A right valve from Puerto Chame, Panama, has a length of nearly 

 n mm. 



Apparently a rare but distinctive species. 



Range — San Salvador to northern Peru. Panama: Panama City 

 (Zetek); Puerto Chame; Guanico. Peru: Tumbez. 



Genus PSA3DIAC03IA Ball, 1900 

 Type species by original designation, Tellina Candida Lamarck (r= 

 galathea Hanley). 



Shell elongate, tagelloid, valves subequal, the posterior side much 

 shorter, weakly flexed, and bluntly truncated at the end. Ligament 

 and resilium attached to a long, narrow scar which is wholly external, no 

 nymphal ridge. Adductor scars subequal. Pallial sinus not extending to the 

 anterior adductor, rounded at the end, free or partly coalescent with the 

 pallial line. Surface smooth except for fine lines of growth and covered 

 by a thin and often radially hirsute periostracum. 



Two subgenera 

 L Entire surface smooth except for the lines of growth. 



Subgenus Psammacoma, s.s. 

 IL Similar but with the posterior slope granulose. 



Subgenus Macoploma 



Psammacoma lamprolenca (Pilsbry and Lowe) Plate 68. fgure 12; 



Plate 74, figures 3-3b 



Tellina lamprolcuca Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 



8+, p. 93, pi. 11, figs. 6, 7 (as Macoma parthenopa Pilsbry and Lowe, p. 144, 



explanation of plate). 

 Macoma (Psammacoma) lamprolcuca (Pilsbry and Lowe), Hertlein and Strong, 19+9, 



Zoologica, vol. 34, pt. 2, No. 9, p. 90. 



Shell generally large (length 75 mm., or more), Tellina-Yike, solid, 

 white under a thin, deciduous, buff-colored periostracum, the anterior side 

 a third longer than the posterior. The right valve is moderately flexed, 

 the zone behind the posterior-umbonal slope is depressed, the posterior 

 area itself flattened and fairly wide; the left valve is more evenly convex, 

 the posterior area narrow, the end turned inward but slightly. Surface 

 smooth with the growth lines fine and indistinct. Interior porcellaneous 

 white, the adductor scars subequal, shiny, the pallial sinus as figured, 

 extends a little beyond the middle and confluent with the pallial line for 

 about a quarter of its length. 



This is a common species in the Panama Canal Zone, especially at Palo 

 Seco and Thatcher's Ferry. It is often large, a specimen from Punta Ostiones 

 in Ecuador measures as follows: length 96.2 mm., height 54.4 mm., semi- 



