102 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



1856. One species with typical incrustation seems to be new to science. 



Key to west American species: 



Incrustation thin, tending to be arranged in 



transverse rows of pustules spatiosa (Carpenter) 



Incrustation loose, chalky, forming a divari- 

 cating pattern on the posterior part hancocki n. sp. 



Lithophaga (Leiosolenus) spatiosa (Carpenter) 1856 

 Plate 10, fig. 59 



Leiosolenus spatiosus Carpenter, Catalogue of the Reigen Collection of 



Mazatlan Mollusca, 1856, pp. 130-131. 

 Syn.: fLithophagus rugiferus Carpenter 1856. 



fLithophaga abbotti Lowe 1935. 

 Holotype: British Museum 

 Type loc: Mazatlan, Sinaloa, Mexico. 



Kemarks: The descriptions of this species and of the subgenus Leiosolenus 

 are very short and based mainly on the chambers made by the boring 

 bivalve. The main characters of the bivalve are the short, bent shell, with 

 well rounded ends, barely angled dorsal margin, and slight excurvature 

 in front. The incrustation is thin, equal over all the surface and tending 

 to be arranged in transverse rows of pustules. It seems to be a large 

 species, though the length of the type, which is supposed to be a young 

 specimen, is only one and a half inches. As far as I can see, this species 

 has not been recognized since it was described by Carpenter; but it is 

 very possible that Lithophagus rugiferus Carpenter and Lithophaga 

 abbotti Lowe should be referred to the same species. 



L. spatiosa represents one of the largest species, with length up to 

 62.5 mm (abbotti Lowe). The incrustation is variable but usually some 

 transverse rows of pustules can be observed on fresh specimens. 

 O ccurrence : The records are from the shore down to 15 fms, boring in 

 valves of Pinctada and Ostrea (rugiferus Carpenter). 

 Distribution: From Ecuador (rugiferus) to San Felipe, Gulf of Cali- 

 fornia (abbotti). 



Lithophaga (Leiosolenus) hancocki new species 

 Plate 10, fig. 60 



Diagnosis: Shell elongate, cylindrical, rather inflated, two and a half to 

 three times as long as the maximal height; umbones nearly terminal, 

 anterior margin rounded, ventral margin nearly straight with a rounded 

 posterior margin, dorsal margin with a more or less distinct median 



