THOMEA. 333 



base there are three thin lamellae, a large parietal, a very 

 large axial, and a very small, oblique axial below. The two 

 larger lamellae extend into the next preceding whorl (fig. 3, 

 a shell 12 mm. long). In a specimen of the Trinidad can- 

 ter 'oiana 12 mm. long there are 14 whorls, while cienfuego- 

 sensis of the same length has but ll 1 /^ to 12 whorls. 



Genus THOMEA Girard. 



Thomea GIRARD, Jornal de Sciencias Math. Phys. e Nat. 

 Acad. Real das Sci. de Lisboa, Ser. 2, iii, p. 106 (1893). 



' ' Shell very small, dextral, turriculate, composed of numer- 

 ous slowly widening whorls, striate, perforate, thin. Whorls 

 convex with well-marked suture. Aperture oval, the colu- 

 mellar margin reflexed, continuous with the peristome, which 

 is simple and acute, with the margins united by a well-defined 

 parietal callus, bearing a parietal lamella visible externally; 

 columella with a fold not visible externally. 



"Radula with a very small central tooth with obsolete 

 cusp; laterals tricuspid; marginals very short, transverse, 

 armed with 4 to 7 cusps. Formula 16, 8, 1, 8, 16. 



"The animal is viviparous, young shells taken from an 

 adult shell measuring 2 mm. long" (Girard). 



Type T. newtoni Girard. Distribution, Island of St. 

 Thome, in the Gulf of Guinea. 



This group might more justly be ranked as a subgenus of 

 Pyrgina, from which it differs only in the reduction of the 

 axial tube to a narrow perforation. 



1. T. NEWTONI Girard. PL 49, figs. 17, 18. 



Shell dextral, long, turriculate, thin, covered with a cor- 

 neous cuticle ; ornamented with longitudinal striae which are 

 quite regular, rather thick, a little sinuous and but slightly 

 oblique. Whorls 12 or 13, slightly convex with well-marked 

 suture, regularly and very slowly increasing. 3y 2 embryonic 

 whorls nearly smooth ; last whorl about one- fourth the total 

 length, a little angular at base. Umbilical perforation nar- 

 row, a little covered by the reflexed, straight columellar bor- 

 der. Aperture oval, a little retracted at base ; peristome with 

 thin, sharp borders, united by a light callus. There is a low 



