GASTEROPODA. 15 



them to that genus. The shells of these species are, in the young state, quite 

 smooth, and have a visible spire, with a sharp and simple outer lip, and it is only 

 when full grown that the mantle envelopes the entire shell, depositing a calcareous 

 coating, by which the spire is hidden, the exterior is covered with transverse ridges, 

 and the outer lip is thickened and inverted. 



The larger and smoother species are inhabitants of tropical or subtropical regions, 

 but, as a genus, it extends from the equator to the coast of Greenland. A species of 

 the section Trivia has been found in the Eocene formations of this country, one 

 specimen of which is in the cabinet of Mr. Wetherell, and another in that of the late 

 Mr. Channing Pcarce. 



" Pig" is the common name of these shells upon the coast. In Italy they are 

 called Porcelli ; and Porcelain, the common name of cowries, is taken from the fancied 

 resemblance of these shells to pigs." — (Gray Zool. Proc. 1832.) 



1. Cypr.^ja avellana. .7. Sow. Tab. II, fig. 5, a — e. 



Cypk.ea avellana. J. Sow. Min. Con. t. 378, fig. 3, 1832. 



Trivia AVELLANA. S. Wood. Catalogue 1842. 



Teivia testudinella, var. (i. S. Wood. Catalogue. 



Cypr^a avellana. Nysf. Coq. foss. deBelg. p. 608, pi. 45, fig. 13, 1844. 



Trivia AVELLANA. Morris. Cat. of Brit. Foss. p. 164, 1843. 



C. Testa ovato-glohosd, crassci, transversim striata, striis plus minusve numerosis, sulco 

 dorsali interrtipfis ; aperturd lineari angmtatd. 



Shell ovato-globose, variable, thick and strong, covered with transverse striae or 

 ridges, more or less numerous, interrupted on the back by a longitudinal sulcus ; aper- 

 ture linear, with the inner lip concave at the lower part. 



Axis, % of an inch. 



Localiti/. Cor. Crag, Sutton. 



Red Crag, Walton and Sutton. 



Rare in the Coralline Crag, but not so in the Red Crag at Walton. It is a 

 very variable species, the length of axis ranging from three fourths to less than one 

 fourth of an inch, with a transverse diameter, in some individuals, equal to its length, 

 while, in others, it does not exceed two thirds of it. The number of ridges upon the 

 exterior varies in almost an equal degree, and affords but little assistance for specific 

 determination. One specimen in my cabinet has as many as forty, while another 

 has only twenty-four ridges. T. testudinella of my Catalogue was the elongated 

 var. (fig. 5, c), which is now united with C. avellana, as I have reason to believe, 

 from the examination of more specimens, that the differences are not specific, and that 

 they may be connected by intermediate forms. It appears distinct from C. affinis, 

 Dujard., in which the costse are more iri'egular, and terminate obtusely, lea\-ing a naked 

 sulcus on the back, while in this species the ridges are continued across it. 



This species is also found in the Touraine beds, specimens of it, from that locality, 

 are in the cabinet of Mr. Lyell. 



