no.1704. A COLLECTION OF SHELLS FROM PERU—DALL. 161 
MESODESMA DONACIUM Lamarck. 
Plate 27, fig. 1. 
5 
Mactra donacia LamMarcx, Anim. s. Vert., vol. 5, 1818, p. 479.—CuENnu, Man. 
de Conchyl., vol. 2, 1862, p. a 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, pl. 471, fig. 12. 
Taken from the rocks at north end of the water front at Callao, and from nullipores 
dredged in 5 fathoms, in Sechura Bay, west of Matacaballa. 
Distribution.—F rom Guayaquil to the Straits of Magellan, boring 
in soft material. 
Shell small, irregular, mostly soihes indica distally blunt or sub- 
truncate, drailes covered with a straw-colored periostracum. 
MARTESIA CURTA Sowerby. 
Pholas curta SowERByY, Proc. Zool. Soc. of London for 1834, p. 71; Thes. Conch., 
vol. 1, 1849, p. 494, pl. 104, figs. 33, 34; pl. 108, fig. 105. 
Boring in driftwood on the mud flats of La Pampa, mouth of the Tumbes River, 
Peru. 
Mstribution.—Almost world-wide in the tropics; boring in floating 
timber; West Indies, Panama, Ecuador, and Peru. 
Shell oval, pomted behind, rounded in front; valves divided by a 
transversely grooved band; the anterior area obliquely divided in 
the adult, the dorsal portion with radiating wrinkles and transverse 
striz, 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 
aowened with a horny cuticle. 
These small borers, except as helping to disintegrate sunken drift- 
wood or wrecks, seem to have no economic importance. 
Proe.N.M.vol.37—_09——11 
