64 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



Occurrence: Living burrowed in mud with the posterior margin above 

 the surface, from the intertidal zone down to 25 fms. A "nest" of mud 

 and sand particles seems to be built like that of M. neglectus, to prevent 

 mud particles from entering the mantle cavity and to anchor the animal 

 in the mud. 



Distribution: Vancouver Island, British Columbia, to Outer Gorda Bank 

 and Bahia Concepcion (Boone, 1928), Baja California. 



Modiolus eiseni Strong and Hertlein 1937 

 Plate 6, fig. 29 



Modiolus eiseni Strong and Hertlein, Proc. Calif. Acad. Sci., vol. 22, 



1937, pp. 160-161, PI. 34, figs. 11, 14-16. 

 Holotype: California Academy of Sciences, no. 6968. 

 Type loc: 38 miles SE of Mazatlan, Sinaloa, Mexico; 10-17 fms. 

 Remarks: This species might perhaps be Modiola biradiata Hanley 1843, 

 but as the locaHty of Hanley's species is doubtful and the description 

 seems to show minor differences, it is safest to use the name given by 

 Strong and Hertlein. Eight small specimens of this typical species were 

 found in the Hancock material, maximal length, 11.5 mm. 



The lunule is dull and rather large and the white prodissoconch is 

 elongate, oblique. The anterior adductor is narrow and follows the an- 

 terior margin. The posterior part of the mantle margins is thickened, the 

 septum short, ending in a rounded knob, and the dorsal opening is elon- 

 gate. 



Occurrence: Recorded from 2 to 50 fms, or to 200 fms if the deepest haul 

 mentioned by Strong and Hertlein is used. The bottom conditions are 

 given as mud, sand, or shells. The Hancock material extends the distri- 

 bution of this species from Mazatlan south to Panama. 

 Distribution: From off Outer Gorda Bank, Gulf of California, to off 

 Bahia Honda, Panama. 



Modiolus neglectus new species 

 Plate 7, figs. 31-32; text-figs. 49, 51, 59 



Syn.: Volsella recta auct. non Conrad 1837. 



Volsella flabellata auct. 7ion Gould 1850. 

 Diagnosis: Shell elongate, inflated, with straight dorsal margin which 

 reaches considerably before the umbo, sharply rounded from the antero- 

 dorsal angle; anterior margin sloping and evenly rounded to the nearly 

 straight ventral margin. Posterodorsal angle rounded, posterior margin 

 slightly convex and meeting the dorsal margin in an angle of about 140°, 



