NO. 2 ROST: THE FAMILY ARCIDAE 193 



Type loc. : Payta, Peru ; under stones. 

 Holotype: British Museum? 



Remarks: Although the West Atlantic species, Arcopsis adamsi (Dall) 

 1886, is very similar to A. solida. Heath (1941) found that the two 

 species differ in several anatomical details. Both species have one pig- 

 mented eye-spot on the anterior end of each mantle margin, just where 

 the two margins join each other dorsally. 



Arcopsis solida attains a length of 20 mm (Maury, 1922, p. 21). 

 The other measurements of the same shell are: height, 14 mm; diameter, 

 14 mm. The D/L ratio increases with increasing length. 

 Occurrence: This species is common in the intertidal zone among 

 shingle, sand, and rocks. It is also often taken in depths down to 30 or 

 40 fms, on bottom of sand, shells, and rocks. 



So far as is known, no living specimens have been taken in Cali- 

 fornia, although Keen (1937) gives its range to 34° N. (See discussion 

 in the Minutes of the Conchological Club of Southern California, no. 

 34, April, 1944, pp. 5-6). Arcopsis solida is commonly confounded in 

 collections with species of the genus Acar, in spite of the fact that the 

 character of the ligament distinguishes the two genera very easily and 

 no confusion should be necessary. 



Distribution: Bahia de Vizcaino, west coast of Baja California, and 

 Gulf of California, to Payta, Peru. The Galapagos Islands. 



Subfamily AnadarinaC Reinhart 1935 



Genus ANADARA Gray 1847 



Anadara Gray, Proc. Zool. Soc. London, 1847, p. 198. 

 Type of genus: Area antiquata Linne 1758 (orig.). 



Remarks: The species of genus Anadara from the region covered in the 

 present paper are placed in four subgenera: Anadara s.s.j Larkinia 

 Reinhart 1935, Scapharca Gray 1847, and Cunearca Dall 1898, in the 

 arrangement used by Reinhart (1943). Anadara s. s. contains equivalve 

 species with an equal sculpture on both valves. Larkinia is distinguished 

 by having teeth converging at the extremities of the hinge but diverging 

 in the center ; it is also described as equivalve, a character which cannot 

 be used for separation, as one species included, Anadara (Larkinia) 

 multicostata (Sowerby), is inequivalve. In Cunearca are found inequi- 

 valve species with strongly discrepant sculpture on the two valves. 

 Scapharca is used for species which do not fit in any of the other sub- 

 genera, or species which fall in between Anadara s. s. and Cunearca. 



