NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 67 



ord from Laguna de San Ignacio may perhaps be founded on specimens 

 of Modiolus americanus (Leach). Small specimens of M. modiolus are at 

 present impossible to identify with certainty. There may be a possibility 

 that the larvae of M. modiolus now and then settle far to the south of the 

 usual habitat and live there for some time, but are unable to establish 

 themselves. Perhaps some of the smooth-haired smaller specimens found 

 south of Monterey are really young M. modiolus. It is to be hoped that 

 some one will study this problem and make it possible to separate young 

 specimens of the various species of Modiolus. 



Occurrence: Living solitary, fastened to rocks, from a few fathoms down 

 to at least 100 fms. 



Distribution: Arctic Ocean to Monterey, California; Japan; Atlantic: 

 south to Florida, and the Mediterranean. 



Modiolus americanus (Leach) 1815 

 Plate 6, figs. 27-28 ; text-fig. 56 



Modiola americana Leach, Zoological Miscellany, vol. 2, 1815, p. 32, 



PI. 72, fig. 1. 

 Syn.: Modiola tulipa Lamarck 1819. 

 Holotype: British Museum? 

 Type he: ? 



Remarks: One small specimen from Ecuador with a total length of 14.5 

 mm seems to be very close to this species. The shell is whitish but fur- 

 nished with six or seven violet radiating striae starting just behind the 

 white irregularly rounded prodissoconch. The anterior margin and the 

 posterodorsal angle are broadly rounded. The periostracum is yellowish- 

 white with fine hairs and adhering particles of shells and sand. The byssus 

 is silklike, yellow. 



Another specimen, from Bahia de Santa Maria, Baja California, with 

 a total length of 29 mm, is brownish-yellow with a violet tinge on the 

 umbones. This specimen is of the same form as the small specimen from 

 Ecuador, but lacks the color rays. In the collections of the California 

 Academy of Sciences, there are two samples of a Modiolus identical with 

 the specimens from Bahia de Santa Maria. They are labelled Mazatlan, 

 Sinaloa, Mexico, beach, no. 27223 (Hertlein collection), maximal length 

 38 mm, and Bahia de la Magdalena, Baja California, no. 20285 (Orcutt 

 collection), maximal length 42 mm. These two samples are exactly like 

 specimens from Clearwater Harbor, Florida, no. 5835. 



Modiolus americatius (Leach) is closely related to the more northern 

 Modiolus modiolus (Linne) but seems to differ in some respects. The shell 



