374 AXEL A. OLSSON 



This is a small, elongate-ovate shell, thin, with nearly median beaks, 

 and a pointed posterior end, a trifle longer than the anterior which is 

 widely rounded. In shape, this small shell is strikingly like Leptomya 

 amencana, and possibly may be merely the young of that species, but the 

 right valve is provided with a set of weak lateral teeth and the resilifer is 

 larger, Cumingia-Yxke. in shape. The species is known only by the type. 



Range — Mexico, Mexico: Guaymas. 



Genus LEPT03ITA A. Adams, 1864 



Type species by subsequent designation, Stoliczka, 1871, Neaera 

 cochlearis Hinds. Recent, Japan, Philippines. 



The shell is generally elongately triangular with elevated pointed beaks, 

 the anterior end rounded, the posterior side pointed at the end. Ligament 

 largely internal, the resilifer in the shape of posteriorly directed groove or 

 pit in the hinge plate, not projecting below it. Hinge with cardinal teeth 

 only; one in the left valve, two small ones in the right. Pallial sinus large, 

 its lower limb confluent with the pallial line. Surface plain or with growth- 

 line striation. 



Leptomya differs from Abra by the generally larger size of its repre- 

 sentive species, its more triangular shape, the absence of lateral teeth and 

 by its simple, grooved resilifer which does not project below the hinge 

 plate. Its species are mainly distributed in the western Pacific. (Japan, 

 Philippines, Australia.) A single species is now known from the eastern 

 Pacific. 



Leptomya ecnadoriana Soot-Ryen Plate 66, figure 5; 



Plate 67, f-gure 5 



Leptomya ecuadoriana Tron Soot-Ryen, 1957, Lunds Universitets Arsskrift. N. F. Avd. 



2, Bd. S3, nr. 10, pp. 10, 11, fig. 2 Puna, outside Guayaquil, Ecuador, 8 fms., 



clay. 

 Leptomya americana A. Keen, 1958, Bull. Amer. Paleont, vol. 38, No. 172, p.246, pi. 



30, figs. 9, 10; pi. 31, figs. 3, 5, 6. 



The shell is of medium size (average about 30 mm.), obliquely ovate- 

 trigonal in shape, Macoma-\ike, thin, white, subequivalve, the posterior end 

 somewhat pointed, the beaks nearly median. The anterior side is higher, 

 inflated or convex across its umbonal slope, its dorsal or lunular submargin 

 somewhat impressed, its end broadly rounded. The posterior side is much 

 narrowed, appearing slightly attenuated, weakly twisted and bluntly pointed 

 at the end, but not longer than the anterior side. Surface of shell is white, 

 usually showing a dull luster which under the lens is found to be due to a 

 thin, chalky, outer layer covered in exceptionally well-preserved specimens 

 with fine granules; under this outer layer (usually destroyed by wear in 

 beach specimens), the surface is smooth, with the growth lines showing 

 indistinctly. Pallial and muscle impressions show indistinctly, but the pallial 

 sinus is large, highest under the beak, rounded in front, not reaching to 

 the anterior adductor scar and united below with the pallial line for three- 

 fourths of its length. The right valve has two small cardinal teeth directly 

 under the beak, the left valve with one; no lateral teeth. 



Length 29.3 mm., height 20.1 mm., diameter 10.6 mm. Puerto Pizarro, 

 Peru. 



