PANAMIC-PACIFIC PELECYPODA 135 



Range — Lower California to Chile. Mexico: San Ignacio Lagoon (Hert- 

 lein and Strong). Costa Rica: Port Parker (Hertlein and Strong). Panama: 

 Guanico. Ecuador: Palmar near Colonche; Manta; Jaramijo. 



Lithophaga (Labis) peruTiana (d'Orbigny) Plate 15, figures 2-2a 



Lithodomus peruvianus d'Orbigny 1846, Voy. Amer. Merid., vol. S, pt. 3, MoUusques, 



p. 651. 

 Modiola atteriuata Philippi, 1847, Abbild. und Beschreib, Conchylien, bd. 2, p. 148, pi. 



1 (Modiola), fig. 6 not of Deshayes. 

 Lithodomus cumingianus Dunker, 1857, in Reeve, Conch. Icon., vol. Lithodomus, pi. 21, 



figs. 8a-b. — Dunker, 1882, Syst. Conch, Cabinet. Lithophaga, p. 5, pi. 2, figs. 9, 



10. — Chenu, 1862, Manuel de Conchyliologie, vol. 2, bivalves, p. 156, fig. 769. 



Shell often quite large, thin, subcylindrical, the ventral margin and 

 the anterior half of the dorsal margin straight and parallel, the posterior 

 section of the dorsal margin descends strongly towards the end. Whole 

 surface is covered by a thin encrustation which thickens near the posterior 

 end, often forming there a short, wedge-shaped point. 



Length 84 mm.; height 22.3 mm.; diameter 23 mm. 



Paracas Peninsula, Peru. 



Since D'Orbigny gave no illustration of this species, some misunder- 

 standing has existed as to its identification. A photograph of a specimen 

 in the type lot at the British Museum (Nat. Hist.) is given here. It differs 

 from atteniiata by its shorter, higher shell, and less attenuated posterior 

 end. It appears to be common along the Peruvian coast south of 

 Lima, where it is often found boring into the massive heads of a colonial 

 polychaete worm (Gunnarea). 



Range — Coast of Peru. Peru: Callao; Paracas Peninsula. 



Lithophaga (Labis) inca (d'Orbigny) Plate 15, figure 1 



Lithodomus inca d'Orbigny, 1846, Voy. Amer. Merid., vol. 5, pt. 3, MoUusques, p. 651 

 Paita. 



The type specimen in the British Museum (Nat. Hist.) is a large 

 shell about 83 mm. in length, thin, with the umbones near the anterior 

 end, convex and full, the anterior margin itself rounded. The posterior side 

 is much elongated, evenly tapering to the end, the urnbonal slope bearing 

 a wide band formed between two shallow lines or sulci, that on the dorsal 

 side simple, that on the ventral side double. The whole surface is covered 

 by a thin calcareous encrustation, smoothish or faintly granulose, thickening 

 at the end to form a flattened beak which projects beyond the valve 

 margins. 



According to D'Orbigny, this species differs from L. peruviana by its 

 more elongate form, more even taper behind, and in having two radiating 

 sulci along its posterior side. The posterior sulci are usually faint but can be 

 found on close examination. The form is questionably distinct from L. 

 attenuata but may perhaps differ by its less cylindrical and more evenly 

 tapering outline as well as having a somewhat higher and more rounded 

 anterior end. 



Range — Paita (Fontaine, D'Orbigny). 



