432 AXEL A. OLSSON 



Aloidis (Caryocorbula) marmorata (Hinds), Hertlein and Strong, 1950, Zoologica, vol. 

 35, pt. 4, pp. 239, 240, pi. 2, fig. 17. 



Shell small, ovately trigonal, nearly equlvalve, whitish, mottled, a 

 purplish-red spot present under the beaks; rounded in front, slightly pro- 

 jecting posteriorly and obliquely truncated at the end, often with a short 

 lamellated projection; a strong posterior angulation marks off a flattish 

 sloping posterior area; an excavated area is present beneath the beaks 

 but only a minute sloping escutcheon is present back of the beaks; sculp- 

 ture consists of strong, often somewhat angular or carinate concentric ribs 

 which continue with equal strength over the posterior area but become 

 finer toward the posterior and anterior dorsal margins; the interspaces and 

 especially the posterior dorsal area is ornamented with fine radial striae; 

 interior often pinkish with well-defined whitish adductor impressions. 

 Length 7 mm., height 4.8 mm., convexity (both valves together) 3.4 mm. 

 Description after Hertlein and Strong, 1950. 



The above description is copied from Hertlein and Strong. C. marmorata 

 is perhaps a small form of C. biradiata. Specimens referred to this species 

 before me, are similar in shape to that species, but much smaller, the sur- 

 face nearly smooth except for a few concentric riblets; these specimens have 

 no radial striae as described by Hertlein and Strong, but radial striae are 

 sometimes to be seen on specimens of C. biradiata. Surface is mottled with 

 blotches of white on a gray-white base, the edge of the beaks and the 

 ventral margins often stained pink. 



Range — Mexico to Ecuador. Mexico: Punta Penasco; Port Guatulco. 

 Nicaragua: Corinto. Costa Rica: Port Parker (these records all from 

 Hertlein and Strong). Panama: Veraguas (Hinds). Ecuador: Santa Elena. 



Subgenus HEXACOKBULA Olsson, 1932 

 Type species by original designation, Corbula hexacyma Pilsbry and 

 Brown. Miocene of Panama. 



Shell moderately large and heavy, the anterior end rounded, the 

 posterior rostrated and pointed. Surface sculpture with deep, wavelike, con- 

 centric ribs, usually sulcated in the middle, and finer lines of growth. No 

 lunule or escutcheon. 



Caryoeorbnia (Hexacorbula) esmeralda, new species Plate 76, figures 3-3c 



The shell is relatively large (length 22 mm.), heavy, transversely ob- 

 long, with nearly median beaks, the anterior end well rounded, the pos- 

 terior side narrower or contracted, with a sloping, flattened or depressed 

 rostral area, its end oblique and pointed. Surface sculpture of each valve 

 is similar, produced by a few, large, wavelike, concentric riblets, their 

 intervals deep, the whole overrun by the much finer growth lines; the 

 concentric riblets are strongest over the anterior middle of the disk, and 

 from there curve smoothly over the umbonal slope to the margin; pos- 

 teriorly they fade out near the rostral angle. On the rostrum, the sculpture 

 is produced by even, close-set, medium-size, cross-concentrics. On some 

 specimens, small radial threadlets may be seen but they are usually incon- 

 spicuous. Old shells may be much thickened, with the ventral margin 

 sharply inflected and flattened; this thickening is largely concentrated along 

 the ventral margin below the pallial line, thereby emphasizing the depth 



