328 GASTROPODA. [Pectinibranchia. 



appendix on each side, in front feebly auriculate or undulate ; mantle 

 sfightly canaliferous on the right upper margin ; a single branchia ; 

 verge subcylindric, elongate. 



Shell turreted, with a plicate axis ; the outer lip frequently 

 internally lirate ; in the larger forms the aperture is obscurely 

 channelled in front ; the larval shell is sinistral, the adult dextral, the 

 former frequently set at an angle to the adult axis, or more or less 

 immersed in the adult apical whorls ; it is usually helicoid and smooth ; 

 the sculpture varies from nothing to ribbed, spirally sulcate or 

 reticulate ; the coloration, when present, usually reddish, brownish, 

 or yellow. Operculum ovoid, paucispiral, with the apex anterior, a 

 thread-like arcuate ridge on the outer side, the inner margin notched 

 in harmony with the plaits of the pillar when present. 



The distribution is world-wide, but the larger forms are mostly 

 tropical. They occur first in the Cretaceous, are numerous in the 

 Tertiary, but perhaps are most fully developed in the existing faunas. 



KEY TO GENERA. 



A. Shell elongate-conic, whorls usually inflated and regularly 



increasing ; the pillar with from 1 to 3 folds, but wanting 



in Eulimella .. .. .. .. .. PYRAMID ELLA, 



B. Shell cylindro-conic, many-whorled, generally slender ; no 



columellar fold ; shell usually smaller than in Pyramidella 



and larger than in Odostomia . . . . . . TURBONILLA- 



C. Shell usually short, few-whorled, subconic or ovate ; colu- 



mellar fold single, varying in strength . . . . ODOSTOMIA. 



Genus 1. PYRAMIDELLA. Lamarck, 1799. 



Pyramidella, Lam., Mem. Soc. Hist. Nat. Paris, 1799, 76. Type : Trochus 

 dolabratus, L. Obeliscus, Humphrey, 1797 (fide Morch, 1852). 



Animal having the tentacles large, ear-shaped, the eyes at their 

 inner bases ; mentum large, flattened, divided by a deep median 

 longitudinal fissure ; foot obtuse. 



Shell with elevated sharp-pointed spire, many-whoried, smooth 

 or axially ribbed ; aperture suboval, entire, rounded in front ; colu- 

 mella straight, with prominent spiral plications ; outer lip sharp, 

 often plicate within. Operculum semicircular, horny, subspiral, the 

 nucleus at the front end, its columellar edge notched to fit the folds of 

 the columella. 



Inhabits mostly tropical seas. 



Fossil. Cretaceous and Tertiary. 



KEY TO SUBGENERAi 





A. Shell without columellar plication . . . . . . EULIMELLA. 



B. Shell with 1 columellar fold . . . . . . . . SYENOLA. 



