THE NAUTILUS. 91 



acters given previously. I have collected gravid females as early 

 as Aug. 31. Glochidia were observed first on Sept. 2, so that 

 the breeding probably begins toward the end of August. Dis- 

 charge of glochidia has been seen from May 11 to May 24, and 

 a single discharging female was found on July 5, probably ex- 

 ceptionally belated. My extreme measurement? of the glochidia 

 are: L. 0.21 to 0.23, H. 0.27 to 0.30 mm. 



EURYNIA (MICROMYA) VANUXEMENSis (LEA). Ortmann, 1. c., 

 p. 530.) 



Anatomy: see Ann. Carn. Mus. 8, '12, p. 342, and NAUTIL. 

 29, '15, p. Co. 



Earliest date for gravid females Sept. 2; for glochidia Sept. 

 17. Discharge from May 15 to May 25. 



(The species of the genus Truncilla will be treated in a sep- 

 arate paper.) 



MODIOLUS DEMISSTJS DILLWIN, IN SAN FRANCISCO BAY. 



BY G. DALLAS HANNA. 



One of the supposedly accidental introductions of animal life 

 from the east to the west coast of North America with the ex- 

 tensive attempts to transplant the oyster was the plicated mus- 

 sel, Modiolus demissus. It was first recorded from the new loca- 

 tion by Stearns in 1899 (NAUTILUS, XIII, p. 86) from specimens 

 collected by R. N. Drake in 1894 at a point "3 miles north of 

 Stanford University, ' ' that is, the southern part of San Fran- 

 cisco Bay. The record was repeated by the same author in 

 April, 1900 (Science, n. s., XI, p. 658). 



"Fine specimens" were again collected, apparently from the 

 same colony, by Doe and Gifford, and recorded by Keep in 

 April, 1901 (NAUTILUS, XIV, p. 115). In his "West Coast 

 Shells," Revised edition, p. 37, 1911, the same author states, 

 " It doubtless came to California with seed oysters which were 

 planted in San Francisco Bay, where it may now be found in 

 considerable numbers." 



