PANAMIC-PACIFIC PELECYPODA 93 



centrlcally marked, its concentric rings bearing small, spinelike denticula- 

 tions, the points of which are directed dorsally, both over the summit of 

 the ribs and in the depths of the interspaces. 



This is quite a different species from Anadara grandis, distinguished 

 easily by its more rhombic form, more numerous ribs and by the peculiar 

 markings of its periostracal layer. The range of the species as given by 

 Hertlein and Strong is from California to Panama, but I have not seen 

 specimens south of Mexico. 



Range — Newport Bay, California, south to Panama, and the Galapagos 

 Islands. 



Subgenus GRAJfDIARCA new subgenus 



Type species Area grandis Broderip and Sowerby. 



Shell large, high trigonal, equivalve, solid, often becoming heavy and 

 ponderous in the adult. Umbones wide and prominent, central, and usually 

 feeble sulcate, bordered posteriorly b}'^ the umbonal ridge at first relatively 

 sharp or angled, later becoming lower and rounded. Beaks small, curved in 

 over a wide, triangular cardinal area. Ligament coarse and heavy, covering 

 the cardinal area completely, the surface of the cardinal area striated with 

 faint, vertical hnes and marked with few to many deep, triangular to 

 lozenge-shaped ligamental grooves. Ribs strong, rectangular in section between 

 deeply grooved interspaces, the summit of the ribs smooth or concentrically 

 wrinkled except on the most anterior ones which are crudely noded. Interior 

 of shell widely and deeply fluted by the ribs around the ventral margin. 

 Hinge teeth small, vertical, in a continuous series. Surface of shell pro- 

 tected by a thick, smooth, black periostracum. 



Like Larkinia but differing by its less truncated posterior side and 

 fewer, plainer ribs. 



Anadara (Grandiarca) grandis (Broderip and Sowerby) 



Plate 7, figures 1, la-lc 



Area grandis Broderip and Sowerby, 1829, Zool. Jour., vol. 4, p. 365. — Reeve, 1844, 



Conch. Icon., vol. 2, Area, pi. 1, fig. 4. 

 Area (Anadara) grandis Broderip and Sowerby, Dall, 1910, Proc. U. S. Nat. Museum, 



vol. 37, No. 1704, pp. 154, 253, pi. 25, figs. 9, 10. 

 Seapharea (Scapharca) grandis (Broderip and Sowerby), Maury, 1922, Paleont. Amer., 



vol. 1, No. 4, p. 194, pi. 3, fig. 13. 

 Anadara (Larkinia) grandis (Broderip and Sowerby), Reinhart, 1943, Special Paper, 



Geol. Soc. America, No. 47, pp. 65, 66, pi. 13, figs. 4-6. — Hertlein and Strong, 



1943, Zoologica, vol. 28, pt. 3, pp. 161, 162.— Frizzell, 1946, lour. Paleont, vol. 



20, No. 1, pp. 41-44.— Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, 



No. 2, pp. 195, 196. 



Shell with the characters described for the subgenus. Ribs about 26 or 

 27, typically square in section, elevated, mostly smooth except on the 

 anterior slope where they are crudely noded, their interspaces deep and flat 

 and of the same width as the ribs. Living specimens have a thick black 

 periostracum as protection against acid waters. 



An average specimen measures: length 105 mm., height 85 mm., 

 diameter 85 mm. Tumbez, Peru. 



This is a common, widely distributed species and often used as food 

 in parts of northern Peru, Ecuador, and Panama, where it is known to the 

 fishermen as "Pato de Buro". Although drift shells may occasionally be 



