198 NATICELLA. 



on the posterior side large, irregular ; that on the anterior small ; 

 palleal impression irregular. — Obs. The Linnean genus Mytilus 

 included the Modiolee, which differ from the Mytili in the rounded 

 anterior side ; and the Pinnae, which are large shells, gaping at 

 the posterior extremity. M. achatinus, fig. 158. 



NiEARA. Gray. A genus composed of Anatina longirostrum, 

 Lam. and other similar species. 



NAIA. Sw. A sub-genus of Castalia, Lam. thus described : 

 '*Oval, cardinal teeth beneath the bosses, and deeply sulcated, 

 C. corrugata. Lam. En. Meth. 248. f. 8, picta. Sw. En. Meth. 

 248. f. 6." Sw. p. 379. 



NANINIA. Gray. A genus composed of the planorbicular species 

 of Helix, with large umbilici, and outer lip thin, included in the 

 sub-genus Helicella, Fer. Ex. H. citrina, fig. 280. 



NASSA. Lam. A genus of small shells united to Buccinum by 

 some authors, but separated by others on account of the little 

 tooth-like projection terminating the columella. N. arcularia, 

 fig. 423. 



NATICA. Brug. Fam. Neritacea, Lam. Hemicyclostomata, Bl. — 

 Bescr. Globose, thick, generally smooth ; spire short, pointed, 

 with few volutions ; aperture semilunar, entire ; outer lip thin ; 

 columellar lip oblique, nearly straight, callous ; umbilicus with a 

 spiral callosity, terminating behind the columella, and sometimes 

 filling up the cavity ; operculum shelly in some species, horny in 

 others ; epidermis thin, light, semitransparent. — Obs. The 

 straight, callous, smooth edge of the columella and the callosity 

 serve to distinguish this genus from Nerita, Neritina, Neritopsis 

 and Helix. Fig. 327, 328. 



NATICARIA. Sw. A sub-genus of Natica, thus described : "Oval; 

 convex above ; umbilicus small, open, placed very near the top of 

 the aperture ; inner lip reflected ; small. N. melanostoma, Mart. 

 189. f. 1926, 1927. cancellata, Sw. lb. 189. f. 1939. bifasciata, 

 Griff. Cuv. l.f. 2." Sw. p. 346. 



NATICELLA. Guild. A sub-genus of Natica, thus described : 

 4 ' Operculum horny ; shell globose, but generally depressed; 



