PANAMIC-PACIFIC PELECYPODA 443 



Subfamily PHOLADEfAE 

 With the characters as described in the key. With three genera and 

 three species regional. 



I. Umbonal rejection septate beneath. 



Genus Pholas 



II. Umbonal reflection separated from the surface of the umbones beneath 

 by an open or empty space. 



A. With a single accessory plate. A protoplax present only. 



Genus Barnea 



B. With two accessory plates, a protoplax and mesoplax. 



Genus Cyrtopleura 



Genus PHOLAS Linn6 

 Type species by subsequent designation, Childrens, 1822, Pholas dactylus 

 Linne. Recent, east Atlantic, and the Mediterranean. 



Shell elongate, white, thin, sculptured by concentric ridges, and sharply 

 noded radial riblets, more or less uniform over the whole surface. Umbonal 

 reflection septate. Accessory plates three in number; a simple or paired 

 protoplax, a transverse mesoplax and a long, narrow metaplax. Anterior 

 end of shell beaked or rounded. 



The genus is divided into three subgenera as follows: 



I. Protoplax fused into a single plate. 



Subgenus Monothyra (not regional) 



II. Protoplax paired. 



A. Anterior side beaked. 



Subgenus Pholas, s.s. (not regional) 



B. Anterior side rounded. 



Subgenus Thovana (American) 



Subgenus THOTANA Gray, 1847 

 Type species by monotypy, Pholas oblongata Say (= P. cam,pechiensis 



Gmelin). West Atlantic. 



Shell with the anterior side rounded, the beak and umbones covered 

 by a rounded marginal reflection, deeply septate beneath. There are three 

 accessory plates, usually lost when the valves are separated. The pro- 

 toplax is longitudinally divided into two parts. Mesoplax small, transverse. 

 The metaplax is long, narrow, and thin. 



With two Recent species, both American, P. campechiensis Gmelin in 

 Atlantic waters, and P. chiloensis Molina in the Pacific. 



Pholas (Thovana) chiloensis Molina Plate 78, figures 4, 4a 



Pholas chiloensis Molina, 1782, Saggio Sulla Storia Naturale de Chili, p. 204 Archi- 

 pelago de Chiloe. 



Pholas Chiloensis var. parva Sowerby, 1834, Proc. Zool. Soc. London, p. 69 Island of 

 Plata. 



Pholas laqueata Sowerby, 1849, Thes. Conch., vol. 2, Pholas, p. 486, pi. 103, figs. 19, 

 20 Isle of Plata. 



Pholas (Dactylina) retifer Morch, 1860, Malak. Blatter, vol. 7, p. 177 Realejo, Nicaragua. 



Pholas dilecta Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 84, p. 

 88, pi. 11, figs. 8, 9.— Maxwell Smith, 1944, Panamic Marine Shells, p. 68, 

 fig. 881. 



Pholas {.Thovana) chiloensis Molina, Turner, 1954, Johnsonia, vol. 3, No. 33», pp. 51-54, 

 pis. 25, 26, 27. 



