116 BULLETIN 181, tWITEiD StTATElS Nu^TlOlNiAlL MUSEUM 



The radula of Potena (Cyclohdkeria) nana has the following for- 

 mula: 3:3:3:3, and the jaw lacks distinct median projections. The 

 verge is situated on the back of the neck behind the tentacles. It is 

 swollen basally and provided with a seminal groove and a very sh^rt 

 simple terminal appendage. 



KEY TO THE SPECIES OF SUBGENUS CYCLOBAKERIA 



Zigzag sculpture absent tryoniana 



Zigzag sculpture present. 



Zigzag sculpture on last whorl feeble. 



Zigzag sculpture on base pronounced novaespei 



Zigzag sculpture on base not pronounced welchi 



Zigzag sculpture on last whorl not feeble. 

 Basal keel strong. 



Last part of base outside of keel with protractively 

 curved cords. 



Shell large, greater diameter more than 25 mm magister 



Shell smaller, greater diameter less than 18 mm nana 



Last part of base outside of keel without protractively 



curved cords dentistigmata 



Basal keel feeble. 



Lamella of operculum very broad, almost touching suc- 

 ceeding whorl chittyi 



Lamella of operculum not very broad, not touching suc- 

 ceeding whorl. 



Whorls slightly concave below summit notatior 



Whorls not slightly concave below summit. 



Spire helicoid yallahsensis 



Spire depressed-helicoid balnearis 



PGTERIA (CYCLOBAKERIA) TRYONIANA (Pilsbry and Brown) 



Plate 16, Figubes 22-24 



1910. Aperostoma (Ptychocochlls) tryoniamim Pilsbry and Beown, Proc. Acad. 

 Nat. Sci. Philadelphia, 1910, pp. 534-535. 



Shell small, helicoid, covered with a golden-brown periostracum. 

 The nucleus consists of a little more than 1.5 well-rounded, smooth 

 turns. The postnuclear whorls are marked by slender, retractively 

 curved, well-raised, rather distantly spaced axial riblets. On the 

 last turn these riblets become less regular in size and spacing. 

 Suture strongly constricted in all the whorls. Periphery well 

 rounded, base strongly rounded, moderately broadly openly umbili- 

 cated, with a mere suggestion of a limiting keel at the outer edge of 

 the umbilicus. The base and the umbilical wall are marked by the 

 continuation of the axial riblets. Aperture circular, decidedly 

 oblique, very slightly angulated at the posterior angle ; peristome thin 

 all around. Operculum typically cyclobakerid. 



