Art- on.} GASTROPODA. 517 



internal. There is no operculum except in the Acteonidce and Lima- 

 cinidtf. The pallial cavity is always well developed, and contains 

 the ctenidium, in part at least; this ctenidium is of the "folded' 

 type. With the exception of the Aplustridcc and Thecosomata, the 

 head is devoid of apparent tentacles, and its dorsal surface forms 

 a digging disc or shield, usually separate from the neck, and with more 

 or less scalloped margins. The edges of the foot (parapodia) are con- 

 tinuous with the ventral face of that organ, and are often transformed 

 into highly developed fins. Posteriorly the mantle forms a large 

 " pallial lobe " under the pallial aperture. The stomach is generally 

 provided with chitinous, or even calcified, masticatory plates. The 

 hermaphrodite genital aperture is connected with the male organ by 

 a ciliated groove, except in Acteon, Lobiycr, and Cavolina longirostris, 

 in which, the spermiduct is a closed tube. The Bullomorpha are 

 swimmers or burrowers. 



Fam. ACTEONIDffi, Ball. 



Animal having a well-developed head-disc, bearing the sessile 

 eyes, and prolonged into triangular processes behind ; lateral epi- 

 podial lobes not developed. Radula composed of many longitudinal 

 rows of teeth, all of the same form. 



Shell entirely external, and capable of containing the entire animal ; 

 spiral, with projecting or depressed spire and moderately numerous 

 whorls, the internal whorl-partitions not absorbed ; surface gene- 

 rally sculptured with spiral punctured grooves ; aperture rounded 

 below, with or without columellar folds. Operculum present. 



KEY TO GENERA. 



A. Columella with a spiral fold. 



a. Shell compact, solid, ovoid, with a short spire ; aperture 

 long, narrow above ; the columella bearing a massive 

 bifid fold . . . . . . . . . . PUPA. 



.. Shell compact, with short spire and large ovate body- 

 whorl : aperture over half the height of the shell, nar- 

 rowed above ; the columella bearing a single simple 

 spiral fold . . . . . . . . . . ACTEON. 



aaa. Shell ovate or ovate-turreted, the spire produced ; 'aperture 

 short, generally less than half the shell's height, ovate 

 or oblong ; columella with a small oblique fold . . LETJCOTINA. 



B. Columella with no distinct spiral fold above ; shell irnperforate, 



or nearly so. 

 a. Shell ovate or oblong, with short spire and long aperture ; 



columella vertical, truncated at the base . . . . BULLINA. 



Genus 1. ACTEON, Montfort. 1810. 



Acteon, Montf., Conch. Syst., ii, 314. Type : .4. tornatilis, L. Actceon, 

 A. Adams, P.Z.S., 1854, 58 ; not Actceon, Oken, 1815. Tornatella, 

 Lamarck, Extr. du Cours de Zool. Mus. Nat. Hist,, 1812, 117. Speo, 

 Risso, Hist, Nat. Eur. Merid., iv, 1826, 235. Kattilla, Silvertrop, 1838. 

 Myesota, Gray, 1847. 



Animal having the cephalic shield squared in front, produced 

 behind in 2 triangular appendages, in front of the bases of which the 



