PANAMIC-PACIFIC PELECYPODA 447 



Genus PARAPHOLAS Conrad, 1848 

 Type species by monotypy, Pholas californica Conrad. California. 



The shell is pholadiform, anteriorly convex, the posterior side tubular 

 and moderately produced. Valves have an anterior beak, below which in the 

 young, there is a large, open gap, closed in the adult by a globose, double, 

 calcareous plate or callum, the umbones and the beaks covered by another 

 large plate (the mesoplax); two other accessory plates (the metaplax and 

 hypoplax) cover the posterior-dorsal and the ventral margins respectively 

 The surface of each valve is crossed by two, radial sulci, the anterior one 

 across the umbone to the ventral margin and it shows plainly in the interior 

 as a rib, its end projecting like a tooth at the margin; a second, smaller 

 sulcus extends across the more posterior portion of disk. In front of the 

 first or principal sulcus, the sculpture is produced by scabrous, radial riblets; 

 in the middle zone between the sulci, the sculpture is mainly concentric; 

 in the posterior portion or behind the second sulcus, the periostracum is 

 raised into small laminae. The anterior-dorsal margin is doubled over in 

 front of the beak and extends back a short distance as a small spur. The 

 internal apophyses, one in each valve, are relatively small and slender. The 

 mollusk lies in a secondary tube or chimney, but not attached to it, com- 

 posed of agglutinated rock grains, produced during the excavation of the 

 bore in hard shale or limestone. 



Parapholas acuminata (Sowerby) Plate 78, figure 5; 



Plate 79, figure 3 



Pholas acuminata Sowerby, 1834, Proc. Zool. Soc. London, p. 70 "Panama, in limestone 



rocics at low water". — Sowerby, 1849, Thes. Conch., vol. 2, p. 492, pi. 105, figs. 



48, 49. 

 Parapholas acuminata (Sowerby), Carpenter, 1857, Cat. Mazatlan Shells, Brit. Mus., 



pp. 12, 13, No. 18.— Maxwell Smith, 1944, Panamic Marine Shells, p. 68, fig. 



872 (as calva Gray in Sowerby). — Turner, 1955, Johnsonia, vol. 3, pp. 128-131, 



pi. 78-80. 



Specimens from Ecuador have a length of nearly 60 mm. The posterior 

 extremity is pointed or acuminate, brownish to nearly black in color, orna- 

 mented by the edges of the concentric lamellae of the periostracum. The 

 internal rib (condyle) formed by the external, umbonal sulcus does not 

 extend beyond the ventral margin in the form of a short spur. The large, 

 shieldlike mesoplax, its edges turned in to fit under the umbonal reflection 

 is well developed. The chimney is generally a well-formed, smooth, fine- 

 grained cement-like tube and attains a length of three inches or more. 



This species is fairly common along the coast of Ecuador boring in 

 Tertiary shale at Manta, Esmeraldas, and other localities. 



Range — Gulf of California to northern Peru. Panama: Guanico. 

 Ecuador: Santa Elena; Manta; Crucitas; Esmeraldas. Peru: Boca Pan. 



Parapholas calva (Sowerby) Plate 79, figure 2; 



Plate 80, figures 5, 5a, 6, 6a 



Pholas calva 'Gray', Sowerby, 1834, Proc. Zool. Soc. London, p. 69 "Perico Island, Pan- 

 ama Bay".— Sowerby, 1849, Thes. Conch., vol. 2, p. 493, pi. 105, figs. 51-53. 



Pholas caha var. nana Sowerby, 1834, Proc. Zool. Soc. London, p. 70 Panama. 



Parapholas bisulcata Conrad, 1850, Proc. Acad. Nat. Sci. Philadelphia, vol. 4, p. 156 

 Lower California and Peru. — Conrad, 1850, Jour. Acad. Nat. Sci. Philadelphia, 

 vol. 1, pt. 4, p. 279, pi. 39, fig. 5. 



Parapholas calva (Sowerby), Turner, 1955, Johnsonia, vol. 3, No. 34, pp. 131-133, pi. 81. 



Apparently rare, and distinguished from P. acuminata by its larger 



