S26 AXEL A. OLSSON 



thin, gray periostracum. The umbones may be smooth or neatly sulcated 

 over a small space. The posterior-dorsal slope narrow, flat, and subtruncated 

 at the end. Pallial sinus small, wide and well rounded. 



Length 53.4 mm., diameter 33.4 mm., semidiameter 7 mm. 



Length 53.8 mm., diameter 32.7 mm., semidiameter 8.7 mm. a left 

 valve. Mompiche, Ecuador. 



A common and widely distributed species. Specimens from the Pliocene 

 of Ecuador are larger than the Recent. 



Range — Guatemala to northern Peru. Panama: Panama City; Guanico. 

 Panama Canal Zone: Palo Seco. Ecuador: Esmeraldas; Mompiche; 

 Charapota; Manta; Santa Elena. Peru: Tumbez; Zorritos; Mancora, 



Genus SPIStJLA Gray, 1837 



Type species by subsequent designation, Gray, 1847, Mactra solida 

 Linne. European Seas. 



Shell ovate, the two ends sometimes nearly alike or the posterior side 

 is the longer. Tensilium visible externally and attached to a small scar 

 along the shell margin behind the beak and separated from the deep, spoon- 

 shaped chondrophore by a narrow space. Adductor scars subequal, the 

 pallial sinus short, rectangular in shape. Lateral teeth and sockets strong, 

 equidistant from the chondrophore, the sides of the teeth usually striated 

 or transversely wrinkled. Surface with concentric growth line sculpture 

 and covered by a thin or thick periostracum. 



Splsnia adamsi, new species Plate 57, figures 7-7c 



Shell small or of medium size, convex, trigonal-ovate, nearly equi- 

 lateral, the anterior side slightly longer and wider, the posterior side 

 shorter, its dorsal area flattened or weakly arched and setoff from the 

 rest of the disk by a weak angle. The umbones are nearly median, convex, 

 and prominent. Hinge typical for the genus, the lateral laminae and their 

 sockets elongate, equidistant from the chondrophore, the face of the lateral 

 teeth smooth or weakly striate. The small tensilium is external, visible 

 from above, and separated from the large pit of the chondrophore by a 

 small space. Surface colored a creamy white, polished, marked with in- 

 distinct lines of growth; on the posterior-dorsal area, the growth lines 

 may join together in forming larger cross riblets. The periostracum is thin, 

 varnish-like, and of a light, yellowish gray color, usually worn off beach 

 specimens. Due to the relative thinness of the shell wall, the adductor 

 scars and pallial sinus show indistinctly, the small pallial sinus extends 

 only a short distance beyond the posterior adductor scar, quadrate at its end. 



Length 36.2 mm., height 27.4 mm., diameter of shell with closed valves 

 17.6 mm. Palo Seco, Panama Canal Zone. Holotype, ANSP 218917. 



This small clam is said to appear on the sand bar at Palo Seco, Panama 

 Canal Zone, and was collected there in fair numbers by Messers. Stewart 

 Jadis and Lee R. Beil. Specimens may attain a length of about 50 mm., but 

 the majority are smaller. 



Range — Panama southward to northern Peru. Panama Canal Zone: 

 Palo Seco. Ecuador: San Francisco; Puerto Callo; Santa Elena. Peru: 

 Zorritos. 



