Occasional Papers of the Museum of Zoology 55 



Whorls: about 51/2 retained. Sculpture (fig. x-33) : low 

 and weak ; closest to grandiensis but much more obscure ; sides 

 of last whorl cancellate or malleate ; even the umbilical sculp- 

 ture low and rounded. Earlier whorls: rather weakly can- 

 cellate. Other characters similar to grandiensis. 



Measurements 

 Shell Aperture Operculum Whorls 



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



male 12.2 54(6.6) 44(5.4) 39(4.7) 87(4.1) 30(3.7) 70(2.6) 5^^ 



male 13.0 52(6.7) 42(5.4) 38(4.9) 94(4.6) 32(4.1) 76(3.1) 5% 

 female 



(type) 16.4 50(8.2) 44(7.1) 37(6.0) 85(5.1) 28(4.6) 75(3.5) 6 



female 17.7 51(9.0) 42(7.5) 36(6.4) 88(5.6) 29(5.2) 79(4.1) 614 



Section Tudora s. s. 



Shell : elongate to obovate conic ; males average smaller than 

 females, but the two sexes markedly intergrade in size. Sculp- 

 ture: very variable; no definite tendency to accentuate the 

 spiral ridges of the umbilical region. Post-embryonic whorls : 

 color bands and spiral sculpture begin on 3rd whorl. Peri- 

 stome: sharp, interrupted on parietal wall; more expanded 

 in columellar than in palatal and basal regions ; parietal angle 

 produced and adjacent upper palatal wall emarginate. Oper- 

 culum: calcareous plate well developed, practically equal in 

 area to horny base ; supporting lamellae high, thickened, and 

 usually confluent ; outer edge of calcareous portion only shal- 

 lowly sulcate. Radula : see megacheilos. 



Monotype: Cyclostoma simile ''Gray" Sowerby. This sec- 

 tion appears to be restricted to the islands of Aruba and 

 Curagao. 



Tudora megacheilos megacheilos (Potiez and Michaud) 



Cyclostoma megacheilos Potiez and Michaud (1838; Gal. Douai, I, p. 

 237, fig. xxiv-9, 10). C. simile "Gray" Sowerby (1843; Thes., fig. xxiv- 

 48, 49). C. mcgacheihm Pfeiffer (1846, Zeit. Mai., 33); first Curasao 

 record. C. meyacliilum and megacheilus Pfr. (1847; Chemn., II, p. G6, 

 fig. ix-18, 19). Tudora similis Gray (1850; Cat. Cycloph., 48) ; monot)T)e 

 of Tudora. Cyclostoma roridiim "Parr." Pfr. (1852; Mon. Pneum. Viv., 



