346 



LOWER INVER TEBRA TES. 



Fig. 447. — Nat'ica hems 

 crawling, showing the 

 very large foot. 



the centre of the inner surface of the shell is a calcareous cup, the shell proper coiTes- 

 pondiiig to the saucer. In habits the members of these genera are much like the 

 species of Crepidula. Among the other genera of the family 

 ma\- be mentioned Infundibuliim, Ccipulus, and Hipjyoni/a: 



The Naticid^ are carnivorous marine snails witli globular 

 shells and an entire half-moon shaped aperture, the outer lip of 

 which is shar|), while the inner one is usually ornamented with 

 a callus deposit which is frequently thick and extensive. The 

 animal has a very large foot, and, when extended, broad folds 

 nearly or quite envelop the whole shell. The tentacles are 

 small, slender, and widely separated, though connected for a 

 portion of their length by a fleshy membrane arising from the 

 top of the head. Eyes may be i^resent or absent ; when jiresent 

 they are placed at the base of the tentacles. 



The genus Natica, with its two hundred species, is distrib- 

 uted all over the world. It has been divided into the sub- 

 genera Neverita, Lmiatia, Mamma, Amaura, etc., which need 

 not be characterized here. All are active predaceous forms, 

 living by preference on sandy bottoms and shores, often stray- 

 ing above low-water mark so that they are left exposed by the 

 receding tide. At such times they usually burrow just be- 

 neath the surface, creating a little hummock of sand. 

 In northern New England the most common species 

 is Xatica {Lunatia) Jteros. It is there the largest 

 littoral univalve, the shell in large specimens attain- 

 ing a diameter of three and a half and a length of 

 five inches. In color the adult shell is ashy gray or 

 brownish, the inside of the aperture being reddish ; 

 but the young are frequently marked with three 

 rows of dark, usually reddish spots. This was for- 

 merly regarded as a distinct species under the name 

 triseriata. South of Cape Cod Natica (jVeverita) 

 duplicata is fully as abundant as the species just 

 named. It may readily be distinguished by the 

 callus which in this species completely covers the 

 umbilicus, as shown in the cut. Natica heros ex- 

 tends south to Georgia, and N. duplicata has been reported from Mexico and Yucatan. 

 Several other species of the genus are found on our eastern coasts. 



The food of Natica is mostly bivalve molluscs. Burrowing through the mud, the 

 snail runs across some unfortunate clam, and immediately the siege begins. Close its 

 valves as tightly as possible, the clam is not secure ; for the snail brings its well-armed 

 lingual ribbon into play and by drawing it across the shell, slightly rotating the body 

 meanwhile, it rasi)S away a ])ortion of the hard calcai'eoiis armor, and in time it makes 

 a hole through to the soft ]iarts, which are then devoured. The hole through the 

 shell is almost perfectly circular, and is bevelled like a countersunk hole made by 

 the artisan. 



The egg masses of the Naticas bear the common name sand-saucers ; they are 

 among the most abundant objects on the sea-shore during the spawning season. The 



Fig. 448. — Natica heros. 



