PANAMIC-PACIFIC PELECYPODA 263 



3. Beaks nearly median, the height of the valve somewhat greater than 

 its length. Posterior margin contracted. Gulf of California. 



C. idloana 



4. Beaks placed in a more anterior position. Posterior side rounded, not 

 contracted. Panama. 



C. jadisi 

 II. Shell smaller (length less than 60 mm.). 



5. Shell convex, its umbones hence large and full. Outline subcircular, 

 the height usually a little more than the length. Pallial sinus deep and 

 narrow, pointed towards the cardinal teeth. 



C. singleyi 



Cyclinella subquadrata (Hanley) Plate 55, figure 2 



Artemis subquadrata Hanley, 1845, Proc. Zool. Soc. London, p. 11 "Santa Elena" re- 

 ference given to "Ind. Test, sup. t. 15, fig. 39". — Reeve, 1850, Conch. Icon., 

 vol. 6, Artemis, pi. 3, fig. 15. — Sowerby, 1852, Thes. Conch., vol. 2, Artemis, 

 pp. 661, 662, No. 24, pi. 141, fig. 27 "Santa Elena, Lobos Islands". 



Shell often large (length 95 mm.), obliquely subrectangular, moder- 

 ately convex or vaulted along a line running from the beak and along the 

 umbonal slope to the posterior-ventral margin, the surface of the posterior 

 submargins more or less depressed. Surface of disk chalky or sculptured 

 with coarse, crowded, concentric threads. Lunule absent or indicated weakly. 

 Hinge with three cardinal teeth in each valve and of which the right pos- 

 terior and the left middle teeth are large and bifid, the others thin, lamellar. 

 Pallial sinus large, placed rather low and extending to about the middle 

 of the cavity. 



Length 68 mm., height 66 mm., semidiameter 15.6 mm. (left valve). 



Length 95 mm., height 85.6 mm., semidiameter 49.6 mm. (left valve), 

 both Bayovar, Peru. 



Range — Ecuador and northern Peru. Ecuador: Santa Elena. Peru: 

 Bay of Sechura; Lobos Islands. 



Cycllnella saccata (Gould) Plate 40, figure 6; 



Plate 42, figures 4, 4a; Plate 43, figures 4, 4a, 6, 6a 



Arthemis saccata Gould, 1851, Proc. Boston Soc. Nat. Hist., vol. 4, p. 91.— Gould, 1853, 

 Boston Jour. Nat. Hist., vol. 6, p. 396, pi. 15, fig. 2 "Mazatlan". 



Cyclinella subquadrata (Hanley), Hertlein and Strong, 1948, Zoologica, vol. 33, pt. 4, 

 pp. 180, 181. (Not of Hanley, 1845). 



Shell fairly large, rounded, dosinoid, white, with a thin, dirty, pale 

 yellow or light brown periostracum, moderately convex, especially in the 

 zone of the umbonal slope extending from the beak to the posterior-ventral 

 margin. The exact outlines of the shell is best illustrated by the figures. 

 Surface is closely striated by fine, concentric growth threads and deeper 

 incised lines of the resting stages forming bands of unequal width, wider 

 on the umbones and narrower below. The shell cavity is moderately deep, 

 with the pallial sinus usually well marked, with a sharply angled point 

 directed upwards towards the hinge and not reaching quite to the center 

 of shell cavity. Adductor scars distinct, unequal, the anterior one narrower 

 and placed just below the end of the hinge plate, the posterior larger and 

 situated low down. Lunule narrowly cordate, defined by an impressed line. 

 Measurements of a specimen: length 78.7 mm., height 72.6 mm., diameter 

 38.5 mm. Panama Bay, Shrimpers from the H. B. Johnson collection. 

 Dimensions given by Gould, length 1 3/5 inches, height 1 1/2 inches, 

 diameter 7/8 inches. 



