[1922 NATURAL SCIENCES OF PHILADELPHIA. 35 



groups, which were not studied in detail, sectional names are 

 sometimes included as synonyms under subgenera or typical 

 sections. Next comes a list of the species in each group from the 

 mainland of North America, with synonomical notes, followed by 

 a description of the radulae of examples studied. 



The following synoptic key shows the main distinguishing 

 characters of the groups studied: 



A. Capituliform complex consisting of a comb-lateral and accessory 



plate Subfamily HelicininaB. 



B. Operculum paucispiral; radula "like Helicina" . .Bourciera. 

 BB. Operculum subspiral to eccentric. 



C. Accessory plate with well-developed wing which invests 

 the base of the comb-lateral so. as to mask its outer 

 cusps; all paired centrals with well-developed cusps; 

 operculum with calcareous plate quite well-developed 

 and forming a complete operculum; horny plate thin, 

 usually amber-colored. 

 D. Operculum subspiral to almost concentric; cusps 

 of centrals very well-developed; cusps of comb- 

 lateral exceptionally long and pointed; accessory 

 plate short and heavy with triangular wing; 

 marginals few (39-43) Hendersonia. 



E. Operculum subspiral with marginal nucleus 



Sect. Hendersonia s. s. 

 EE. Operculum subspiral with submarginal nucleus 



Sect. Miluna. 

 EEE. Operculum -almost concentric, with nearly 



central nucleus Sect. Waldemaria. 



DD. Operculum eccentric with nucleus near middle of 

 columellar margin; cusps of C-central somewhat 

 reduced; accessory plate longer; marginals more 

 numerous (52-123) Oligyra. 



F. A and B centrals not developing heavy backs; 



comb-lateral with few, sharp-pointed cusps 

 (6-7) ; operculum light with point and corres- 

 ponding lip-notch poorly developed 



Subgenus Oligyra s. s. 



G. A and B centrals like Hendersonia; accessory 

 plate with wing slightly reduced, so as to 

 show lanceolate outline jmarginals quite strictly 

 ligulate; shell depressed with heavy lip 



Section Oligyra s. s. 



GG. A-central with tendency to reduce the 

 number of cusps, which are borne on the 

 extreme outer tip; marginals with wing-like 

 expansions below the tips, and with number 



