252 Mr. J. Lycett on the Fossil Conchology of the 



the form is a longer oval and much less elevated, the apex being 

 slightly turned to the right side, constituting the Patella ancil- 

 loides of the f Mineral Conchology/ which species should there- 

 fore be expunged. Patella Aubentonensis (Archiac) occasionally 

 loses its strise altogether, and this change is not confined to any 

 particular size or form of shell. Patella nana in advanced age is 

 spread out more horizontally towards its borders, and forms a 

 concave conical and ovate shell. The fine encircling strise then 

 altogether disappear ; the minute figure in the ( Mineral Concho- 

 logy ' refers to the shell in its young state. 



The genus Nerinea is represented by upwards of fourteen 

 species, of which five are abundant ; they seem to occupy in the 

 oolitic rocks the place of the Cerithia of the older tertiary strata, 

 and are decidedly the predominating univalve of their period. 

 Our most common species are destitute of the tubercles or striae 

 by which these shells are usually ornamented ; four only of the 

 species appear to have been figured or described. One fact in 

 connexion with the extinct carnivorous trachelipods should be 

 noticed. The recent genera of that class are furnished with a 

 tubular boring apparatus, by means of which they drill round 

 holes in the bivalves- and prey upon their juices. As none of 

 the oolitic bivalves have such perforations, we may conclude that 

 the extinct carnivorous genera of that period were differently 

 constituted. 



Of the Naticce we number fourteen species, seven of which are 

 new; although the species are thus numerous, one only, N. 

 Michelini (Archiac), is at all common. 



The family of the winged shells, or Strombida, are represented 

 by upwards of eleven species belonging to the same genus ; the 

 greater number of these likewise occur even to the base of the 

 formation. We have separated them from the Rostellarias and 

 Pteroceras under the generic term Rostrotrema ; they are distin- 

 guished from the true Rostellarias by the absence of an upper or 

 posterior siphon upon the spire, the outer lip not extending be- 

 yond the body-whorl or but slightly upon the penultimate, and 

 there is no corresponding thickening upon the inner lip to form 

 a channel. It is true that one or two recent species of Rostellaria 

 have no posterior siphon upon the spire, but in such instances 

 the siphon is present and coiled round upon the upper part 

 of the wing. From Strombus it is sufficiently distinguished by the 

 absence of the sinus on the outer lip. We venture to suggest 

 that the Strombida require a re-arrangement, the digitations of 

 the outer lip not being of sufficient importance to found upon 

 them generic distinctions ; they are of too variable a character, 

 and in some instances depend very much upon the age of the 

 specimen. 



