PANAMIC-PACIFIC PELECYPODA 303 



more produced and pointed. Lunule cordate but little sunken, bounded by 

 a sharp line. External sculpture is formed by even, close set, erect laminae 

 with small but numerous racial threads in their mtervals and on the ven- 

 tral face of the laminae. The lunule and the posterior-dorsal submargin 

 is lammate-striate but without radial sculpture. Surface usually marked 

 with a beautitul pattern of zigzag brown lines, sparse or profusely developed, 

 on a cream-colored base, the lunule generally a solid brown, the posterior 

 dorsal submargin generally heavily maculated. Some shells may be pure 

 cinnamon brown as m the type. Interior white or irregularly blotched with 

 purple or violet. Inner margm of valve finely crenulated. 



Length 44.7 mm., height 35.5 mm., diameter 25.5 mm. Type. 



Length 37 mm., height 26.4 mm., diameter 22.3 mm. Venado Beach, 

 Panama Canal Zone. 



This lovely species is quite distinct from C. ■pulicaria with which it has 

 sometimes been associated, differing by its thinner, much smaller size, more 

 elongated posterior end and its pattern of zigzag brown lines is usually 

 much stronger, although an occasional shell may be colored uniformly with- 

 out any additional markings. The species appears to be local, most abundant 

 in the Panama Canal Zone and vicinity. 



Range — Costa Rica and Panama. Panama: Bahia Honda near Las 

 Tablas. Panama Canal Zone: Palo Seco; Venado Beach. Costa Rica: 

 Puntarenas (Pilsbry and Lowe). 



G&nus NOTOCHIONE Hertlein and Strong. 1948 



Type species by original designation, Venus columbiensis Sowerby. 



The shell is subovate to subcircular, solid, convex, the surface sculp- 

 tured with large, coarse, rounded to flat-topped, radial ribs separated by 

 grooved interspaces, the whole crossed by widely spaced, even concentric, 

 raised cords, strong on the sides but more or less subobsolete along the pos- 

 terior-umbonal slope. The lunule is small, cordate, marked with concentric 

 lines and circumscribed by an incised line which cuts deeply into the an- 

 terior margin, thereby setting off the slightly vaulted surface of the lunule 

 more sharply. The escutcheon is narrow and flat, bordered by a sharp angle 

 in the left valve; in the right valve, the escutcheon is absent and the margin 

 is merely rounded. The hinge plate is heavy, with three cardinal teeth in 

 each valve of which the left, middle tooth is bifid; the right anterior cardinal 

 tooth is small. The pallial sinus is short but distinct. The margins are crenu- 

 lated except on the posterior side. 



Notochione columbiensis (Sowerby) Plate 41. figure 6; 



Plate 52, figures 1-lb 



Venus columbiensis Sowerby, 1835, Proc. Zool. Soc. London, p. 21 Santa Elena. — 



Sowerby, 1853, Thes. Conch, vol. 2, p. 713, pi. 155, figs. 53, 54.— Reeve, 1863, 



Conch. Icon., vol. 14, Venus, pi. 15, figs. 61t, 61b. 

 Chione {Timoctea) columbiensis (Sowerby), Dall, 1909, Proc. U. S. Nat. Museum, vol. 



37, No. 1704, p. 268.— Maxwell Smith, 1944, Panamic Marine Shells, p. 61, 



fig. 786. 

 Chione (Notochione) columbiensis (Sowerby), Hertlein and Strong, 1948, Zoologica. 



vol. 33. pt. 4, No. 13, p. 188. 



Shell coarse and heavy, often nearly round, the beaks placed near the 

 anterior one-fourth, moderately convex. There are about 37, strong, flat to 

 slightly rounded, radial ribs, close-set and uniform over most of the surface, 

 except for about eight on the posterior slope which are smaller and the 



