214 c^ciD^. 



Carpenter established the sections Elephantidum, Anellum 

 and Fartulum^ but De Folin rejects these, because they are not 

 in harmony with all the forms included in them and are insuffi- 

 cient to meet the present demands of science ; he proposes 

 instead : — 



Section I. Levia. Shells smooth. 



Section II. Annulata. Shells annulated. 



Section III! Costulata. Shells ribbed longitudinally. 



Section lY. Quadrilata. Shells cancellated. 



Section Y, Armata. Shells spinose. 



Subgenus Meioceras, Carpenter, 1858. 



Young shell loosely spiral, not in one plane (PI. 66, fig. 43); 

 the adult truncate behind, something like a cow's-horn, some- 

 what inflated, smooth, aperture oblique; operculum externally 

 concave, 



Most of the species occur on the east coast of America between 

 Florida and Rio de la Plata. 



Subgenus Streblooeras, Carpenter, 1858. 



Shell not decollated and without septa, the permanent spiral 

 nucleus lying in a plane obliquely perpendicular to the adult 

 tube (PI. 66, figs. 44, 45). Mostly fossil. 



Subgenus Watsonia, de Folin, 1819. 



Nucleus caducous, tube scarcely curved, conical, aperture 

 round, very oblique, encircled by a strong rib. 



Subgenus Parastrophia, de Folin, 1869. 



Shell tabular, with a scarcely spiral and entirely posterior 

 pointed nucleus, the embryonic shell only having disappeared, 

 anterior part of tube infiated (PI. 66, f. 46). 



Moreletia, de Folin, 1868 (not Gray, 1855), and Spirolidium 

 Costa (in part), are sj-nonyms. 



The feature of this group is the persistence of the second or 

 adolescent stage of growth, in the adult typical Caecum alwa3-s 

 lost by truncation. The posterior end is septate, but pointed. 



