GASTEROPODA. 141 



possessing a calcareous operculum, and also those with a corneous one, and says (En. 

 Moll. Sic. vol. i, p. 161) that they present a similar structure. The Crag formations 

 contain species that possessed a calcareous operculum, as well as those in which the 

 operculum was, no doubt, of a corneous texture, and they are here considered as 

 constituting only one genus. This genus is placed among the circular mouthed, or 

 what are generally considered as phytophagous animals, although some of the species 

 are not only carnivorous, but exceedingly voracious. Some species are found in deep 

 water, while others bury themselves in sand, above low-water mark. It may be con- 

 sidered as a marine genus, though specimens are occasionally found fossil, in estuaiy 

 deposits. 



Sect. a. OPERCULUM CORNEOUS. 

 1. Natica catenoides. S. Wood. Tab. XVI, fig. 10, a, b, c. 



Natica catenoides. .S. Wood. Catal. in An. and Mag. Nat. Hist. 1842, p. 529. 



— GLAUCINOIDES. J. Sow. Min. Conch, t. 479, fig. 4, bene. 



— SowEHBYi (?). Nyst. Coq. foss. de Belg. pi. 37, fig. 31, 1844. 



N. Testa ovato-glohosd, ventricosd, lavi, polifd ; anfractibics 5- — 6, tumidis, depressis ; 

 spird productiusmld ; aperturd ellipticd, obliqud ; umbilico medioeri aperto. 



Shell globose, or ventricosely ovate, smooth, and glossy ; spire slightly produced ; 

 volutions about five, depressed, a little flattened at the upper part ; aperture elliptical, 

 with a moderate umbilicus, open and deep ; lower part of the left lip slightly reflected 

 and callous. 



Longest diameter, 2 inches. 



Locality. Red Crag, Sutton and Walton. 



This species is by no means rare. I have never seen a specimen that has not in 

 some degree been altered by the removal of its glossy outer coating, under which there 

 is a striated surface, and the specimen figured is in that condition ; but portions of 

 that %atreous covering may occasionally be seen, and the shell in its original state was 

 perfectly smooth and polished. The spire is very slightly elevated, with scarcely any 

 depression at the suture, but the upper part of the volution is a little flattened. I 

 have not any specimens that show such an elevated spire and depressed suture as is 

 represented in the Belgian fossil of what I presume to be this species, except those 

 which are much decorticated at the suture. Our shell is more in form like the N. Alderi, 

 and might possibly be a large variety of that species. I think it is specifically distinct 

 from N. catena, which has a more elevated spire. Among all my specimens there is 

 only one which has the umbilicus perfect, and in it the shell is rather roughly striated, 

 as it is also in N. catena, where there is a slight callosity at the lower part of the 

 left lip. 



The young of this species so much resembles N. Alderi, that it is extremely difficult 



