NO. 1704. A COLLECTION OF SHELLl^ FROM PERU— BALL. 161 



MESODESMA DONACIUM Lamarck. 



Plate 27, fig. 1. 



Mactra donacia Lamarck, Anini. s. Vert., vt)l. 5, 1818, p. 479. — Chenu, Man. 

 de Conchyl., vol. 2, 1862, p. 79, fig. 341. 

 Almejas. Ancon. Used for food and bait. Seen not infrequently but irregularly 

 in the market. Also obtained at Mollendo and Sechura Bay. 



Distribution. — Whole Peruvian province, from Valparaiso north to 

 Sechura Bay. 



Shell white, solid, covered with a straw-colored periostracum ; 

 smooth or concentrically obscurely striated; wedge shaped, very 

 inequilateral; shorter end subtruncate, longer end compressed, 

 rounded, much produced. 



This is the type of the genus Mesodesma. 



SAXICAVA SOLIDA Sowerby. 



Saxicava solida Sowerby, Proc. Zool. Soc. of London for 1834, p. 88; Thes. Conch., 

 vol. 4, 1884, p. 133, pi. 471, fig. 12. 

 Taken from the rocks at north end of the water front at Callao, and from nuUipores 

 dredged in 5 fathoms, in Sechura Bay, west of Matacaballa. 



Distribution . — From Guayaquil to the Straits of Magellan, boring 

 in soft material. 



Shell small, irregular, mostly subcylindrical, distally blunt or sub- 

 truncate, chalky, covered with a straw-colored periostracum. 



MARTESIA CURTA Sowerby. 



Pholas curta Sowerby, Proc. Zool. Soc. of London for 1834, p. 71; Thes. Conch., 

 vol. 1, 1849, p. 494, pi. 104, figs. 33, 34; pi. 108, fig. 105. 



Boring in driftwood on the mud flats of La Pampa, mouth of the Tumbes River, 

 Peru. 



Distribution. — Almost world-wide in the tropics; boring in floating 

 timber; West Indies, Panama, Ecuador, and Peru. 



wShell oval, pointed behind, rounded in front; valves divided by a 

 transversely grooved band; the anterior area obliquely divided in 

 the adult, the dorsal portion with radiating wTinkles and transverse 

 striae, the ventral thinner and inflated, only filling the anterior wide 

 gape when the shell is mature; posterior part of the valves concen- 

 trically striated; an accessory piece over the beaks on the back of the 

 shell, pointed distally and contracted in the middle; posterior gape 

 covered with a horny cuticle. 



These small borers, except as helping to disintegrate sunken drift- 

 wood or wrecks, seem to have no economic importance. 



Proc.X.M.vol.ST— 09 11 



