THE NAUTILUS. 107 



of which (May 13) had glochidia, the others eggs. Additional 

 specimens, the females not charged, were found on Sept. 7 and 

 8, 1914 in Clinch River at Clinton and Edgemoor, Anderson 

 Co., Tenn. 



This shell has been taken by Simpson (1. c. ) for a form 

 allied to Anodonta, and I have accepted this view, and have 

 treated the genus Lastena with the subfamily Anodontincs (Ann. 

 Carnegie Mus. S. 1912 p. 297); but in the description (p. 298) 

 of the soft parts of the sterile female, I have called attention to 

 the fact, that typical Anodontine characters have not been ob- 

 served in the marsupial gills : there were no traces of lateral 

 water tubes, and no thickened tissue at the edge. 



The present specimens show conclusively that Lastena does 

 not belong to the Anodontina, but that it is a member of the 

 subfamily Union inse. Also the fact that in May females with 

 eggs were found, indicates that this is a tachytictic form (sum- 

 mer breeder), and not a bradytictic, as the Anodontina are. 



My previous description, as far as it concerns the anal and 

 supraanal openings, the branchial opening, the palpi and gen- 

 eral features of the gills, is confirmed by the present material. 

 To this, however, should be added the peculiar shape of the foot, 



described by Simpson as : "very large club shaped, 



capable of great extension ". This is a very important charac- 

 ter of the genus, and is found in no other North American Naiad, 

 and in this feature Lastena can be compared onl} 1 with the 

 South American Mycetopoda, which, however, belongs to an 

 entirely different family. When contracted, the foot does not 

 show its remarkable features ; but in life, when extended, it is 

 extremely elongated, at least as long as the shell, of subcylin- 

 drical, somewhat compressed shape, with a distal swelling. 

 Apparently, the foot serves as a permanent anchor, and is not 

 withdrawn into the shell under ordinary circumstances, even 

 when the shell is closed, and hence the closed shell is gaping at 

 the anterior end. 



The marsupium of Lastena lata is restricted to the outer gills, 

 and not the whole outer gill is marsupial, but only the middle 

 portion of it, about one half of the length of the gill. The an- 

 terior and posterior sections remain non-marsupial. The 



