NATICID^. 211 



relation of tliis species to the last appears to be nearly 

 similar to that which Tellina pusilla bears to T. do- 

 nacina. 



Family XX. NATI'CID^, Swainson. 



Body spirallj? rolled into a more or less globular form : mantle 

 rather thin : smut (or mentum) wedge-shaped, forming part 

 of the front lobe of the foot : proboscis long and retractile, 

 usually concealed : tentacles triangular, flattened, and pointed, 

 widely separated, and pressed against the front of the shell by 

 the anterior flap or extension of the foot : eyes either immersed 

 in the skin (one at the outer base of each tentacle, and very 

 small) or wanting: foot thick and largely developed, folded 

 back over the front of the shell in the shape of a broad flap or 

 hood, and behind over the base of the shell, so as to cover the 

 greater part of it : gills divided into 2 plumes : odontophore, 

 or lingual riband, short and straight [rhachis 1 -toothed ; pleurae 

 having 3 uncini (Loven)]. Sexes distinct : verge sickle-shaped. 



Shell globular or inclined to oval, smooth or finely striated 

 in a spiral direction : spire blunt, usually very short: epidermis 

 slight: mouth large, semicircular: outer lip thin: operculum 

 ear-shaped and few-whorled, with the spire on the inner side 

 of the mouth, near the base of the pillar. 



In general aspect the animal resembles that of the 

 Bullid(E, especially in the hood-like expansion of the 

 foot in front. But other parts, as well as the shell, are 

 dissimilar ; so that the relation of the two families may 

 be merely one of analogy, such as occurs in many 

 distinct groups of the MoUusca whose habits of life are 

 the same. Both these families are zoophagoLis. The 

 Naticidce live in sand. While preying on weaker shell- 

 fish, they are in their turn devoured by the flounder, 

 haddock, and cod. It is geologically an ancient family, 

 dating (according to M. Pictet) from the upper Silurian 

 epoch. De Blainville called it Hemicyclostoma, Menke 

 Sigaretea, 



