103 



taine. The development of the cup appears to be arrested in 

 this group ; but I am inclined to believe that this is not always 

 the case. 



Genus CALYPTRJ3A, Lam., 1799. 



Shell conical, trochiform, with central, spiral apex, aperture 

 basal, circular, entire ; interior furnished with a spiral diaphragm, 

 the columellar margin of which is twisted, forming a false 

 umbilicus, free margin convex. 



The animal (PI. 30, fig. 7) has a short head, the muzzle bilobed, 

 tentacles rather short, cylindrical, with the eyes on tubercles 

 at their exterior base ; foot short, rounded, obtuse behind, angu- 

 lar in front. 



Dentition, PI. 30, fig. 3. 



The recent species are tropical and subtropical in their distri- 

 bution ; fossil, the genus first appears in the lower Cretaceous. 

 Galerus, Humphrey, 1797, and Mitella, Leach, are synonyms. 



Subgenus GALEROPSIS, Conrad. 

 Spire more elevated. O. excentricus, Gabb. Eocene. 



Subgenus INFUNDIBULUM, Montfort, 1810. 



Summit central, whorls plicate, axis imperforate. 



Tropical and subtropical. Found in the tertiary of the United 

 States and West Indies. Trochita, Schum., 1817, Trochatella, 

 Lesson, 1830, and Clypeola, Gray, 1867, are synonyms. 



Subgenus SIGAPATELLA, Lesson, 1830. 



Shell oval with lateral apex, interior plate with submarginal 

 axis, the free margin concave. Haliotoidea, Swains., 1840, and 

 Trochella, Gray, 1867, are synonyms. 



Genus CREPIDULA, Lam., 1799. 



Shell oval, limpet-like, with a posterior, generally lateral spiral 

 apex ; interior with a lamina or shelf, covering the posterior half 

 of the aperture. 



Animal with head depressed, laterally dilated, muzzle 'short, 

 bilobed, tentacles short, subulate ; foot short, subtruncate in 

 front, rounded behind. 



Dentition, PI. 30, fig. 4. 



