No. 1704. A COLLECTION OF SHELLS FROM PERU—DALL. 153 
Shell slender, arcuate, of a pale brownish-white color (more or less 
bleached ?) with some purple undertones dorsally; moderately tumid, 
with nearly terminal, very inconspicuous adjacent beaks; dorsal 
margin arcuate, very slightly subangulate at the end of the hinge line; 
posterior end rounded; anterior attenuated ‘and rounded; base 
flattish and excavated or subconcave; bounded above by an obscure 
ridge; interior very pearly, of a lurid brown color, especially near 
the hinder edge, paler in the anterior region; shell margins simple; 
anterior adductor scar triangular, small, and deep; posterior scar 
larger, less impressed and near the posterior end of the shell. The 
type (Cat. No. 207756, U.S.N.M.) measured: Length of shell, 65; 
height at middle, 21; diameter at middle, 18 mm. 
The nearest species to*this is Carpenter’s Modiolus mutabilis, 
which, however, is not arcuate to any conspicuous extent and has 
a different basal profile. It is also in all probability when adult a 
much larger shell. 
MODIOLUS PURPURATUS Lamarck. 
Modiola purpurata Lamarck, Anim. s. Vert., vol. 6, pt. 1, 1819, p. 113. 
Modiola ovalis CLessin, Martini Chemnitz, Conch. Cab., 2d ed., 1889, Mytilacea, 
p-. 125, pl. 33, figs. 4, 5. 
Choro. Callao Bay, island of San Lorenzo, on rocks; also at Estero Zarumilla on the 
Ecuador border, near Capon. 
Dstribution.—From Punta Arenas, Chile, north to Ecuador, on 
the rocky shores of the whole Peruvian province. 
Shell smiall, oval, coarsely radiately grooved, black or blackish 
purple with a thick periostracum, solid, angular anteriorly; interior 
purple, the margin crenate, not denticulate near the hinge; the con- 
centric incremental lines sometimes crenulate the radial ridges. 
This small shell has no economic value, but is abundant on the 
rocky beaches. The beaks are often badly eroded. 
LITHOPHAGA (MYOFORCEPS) ARISTATA Dillwyn. 
Mytilus aristatus Dituwyn, Descr. Cat. Rec. Shells, vol. 1, 1817, p. 303.—Woop, 
Ind. Test., 1828, pl. 12, fig. 8. 
Taken in dredge about halfway between Bayovar and Matacaballa, Sechura Bay. 
Distribution.—Red Sea, West Africa, West Indies, the west coast 
of America from the Gulf of California south to Chile, boring in coral, 
[me rock, and nullipores. 
Shell small, slender, thin, nearly cylindrical, rounded and blunt in 
front, pointed behind; the surface is covered with a thin brown 
periostracum beneath which the shell is white; it deposits the cal- 
careous matter from its boring on the exterior of the posterior end 
of the shell, forming a smooth coating which is extended on each 
valve beyond the end of the valve into a point; these points pass 
by each other like the blades of a pair of scissors. 
