44 University of Michigan 



Measurements 



Shell Aperture Operculum "Wliorls 



alt. maj.diam. min.diam. alt. diam. long wide 



male 7.4 53(3.9) 42(3.1) 27(2.0) 95(1.9) 27(2.0) 90(1.8) 4 

 female 



(type) 8.8 51(4.5) 41(3.6) 27(2.4) 96(2.3) 26(2.3) 91(2.1) 4 



B3. Infrequent (9 specimens collected). The type locality. 



B4. Quite common (84 adults). Shells larger than those from B5. 



B5. Frequent (51 adults). Lot measured (see Table IV). 



B6. Quite infrequent (15 adults). Large, light colored. 



BS. Quite infrequent (16 adults). Like B5 in size. 



Subgenus Tudora s. s. 



Shell : larger and heavier than in Bonairea. Post-embryonic 

 whorl : horn-colored, with fine, regular and quite elosely-spaeed 

 growth-riblets ; all apical whorls high, eonvexly rounded and 

 with well-impressed sutures. Aperture: ovoid. Peristome: 

 incomplete to almost continuous; sharp; simply thickened or 

 expanded. 



Operculum: ovoid; nucleus markedly eccentric; external 

 surface of calcareous plate almost flat to concave. 



Radula: cusps of outer lateral are simply spatulate lobes 

 of reflected portion. 



Section Tudorata, new 



Shell: elongate-conic. Males markedly smaller than the 

 females ; the two sexes scarcely intergrade in size. Sculpture : 

 very variable, but always with a marked tendency to accen- 

 tuate the spiral cords in the umbilical region. Post-embryonic 

 whorls: color bands and spiral sculpture begin at about the 

 fourth whorl. Peristome : sharp ; simple, or gradually ex- 

 panded in the palatal and basal regions but abruptly narrowed 

 in the columellar. 



Operculum: chondroid plate slightly concave internally; 

 calcareous plate rather thin, much smaller than the horny 

 base; supporting lamellae not greatly thickened and usually 

 incomplete, so as to leave a considerable sulcus around the 

 outer edge of the calcareous portion. 



