NO. 1704. A COLLECTION OF SHELLS FROM PERU— DALE. 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 mutahilis, 

 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, ji. 113. 

 Modiola ovalis Clessin, Martini Chemnitz, Couch. Cab., 2d ed., 1889, Mytilacea, 

 p. 125, pi. 33, figs. 4, 5. 

 Choro. Callao Bay, island of San Lorenzo, on rocks; also at Estero Zarumilla on the 

 Ecuador border, near Capon. 



Distribution. — From Punta Arenas, Chile, nortli to Ecuador, on 

 the rocky shores of the whole Peruvian province. 



Shell small, 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 ridses. 



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 Dillwyn, Descr. Cat. Rec. Shells, vol. 1, 1817, p. 303. — ^W^ood, 

 Ind. Test., 1828, pi. 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, 

 lime 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 bej^ond the end of the valve into a point; these points pass 

 by each other like the blades of a pair of scissors. 



