NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 103 



angle. Periostracum light, yellowish-brown. The whole surface covered 

 by a loose chalky incrustation ; the triangle from the umbo to the posterior 

 margin bounded by an indistinct ventral furrow and a very shallow dorsal 

 depression, with an incrustation which forms a divaricating pattern and 

 is more solid toward the posterior margin, where it generally projects 

 slightly beyond the valve, with irregular granulated margins. 



Anterior retractor relatively short, posterior retractor above the adduc- 

 tor, which is as far from the posterior margin as one and a half times its 

 own length. Nymphae and resilial list narrow and weak. The maximal 

 length is 38 mm. 

 Holotype: Allan Hancock Foundation. Measurements: length, 32 mm; 



height, 10.8 mm; diameter, 10 mm. 

 Type loc: Isla Onslow, north of Isla Floreana (Charles Island), the 



Galapagos Islands (804-38). 

 Remarks: The loose, often rather thick, incrustation, especially on the 

 anterodorsal part, and the divaricate pattern on the posterodorsal 

 triangle, together with the lack of projecting parts of the incrustation, 

 are characters which make the recognition of this species very easy. As 

 far as can be seen, no other species of Lithophaga combining these char- 

 acters has been described, though the new species seems to be very like 

 a Japanese species reported as L. lima Lamy 1919, a Red Sea species. 



It is a pleasure to dedicate this species to Captain Allan Hancock, 

 whose interest in the exploration of the marine life in the eastern Pacific 

 has made this rich collection possible. 



Occurrence: Fifty two specimens out of a total of sixty nine were found 

 in the crater on Isla Onslow, Galapagos Islands, apparently boring into 

 loose coral (Pavona) in shallow water. One specimen was taken at a 

 depth of 13 fms, on rocky bottom. Three typical specimens from Isla 

 Taboguilla, Panama, from the Lowe collection, are preserved in the San 

 Diego Museum (cat. no. 28374, C. A. Reed leg.). 

 Distribution : The Galapagos Islands; Panama. 



