GASTEROPODA. 141 



the animals of species 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 phyto- 

 phagous 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 considered as a marine 

 genus, though specimens are occasionally found fossil, in estuary deposits. 



Sect. a. OPERCULUM CORNEOUS. 

 1. Natica catenoides. 8. 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. 



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



N. Testa ovato-globosd, ventricosd, lavi, politd; avfractibus 5 — 6, tumidis, depressis ; 

 spird productiusculd ; aperture! ellipticd, obliqud ; umbilico mediocri aperto. 



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

 duced ; 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 vitreous 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 



