102 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 7, 



have broken througli all the boundaries of the genus laid down by 

 M. Deshayes, and admitted many species which do not come under 

 his definition of Nerincea. Voltz, who has added largely to our 

 knowledge of the species, includes in Nerincea shells mth a rhom- 

 boidal mouth and at least one internal fold (Jahrbuch, 1836, p. 538), 

 thus admitting N. grandis and N. depressa, which have only a fold 

 on the columella, and have the outer lip simple : in this he is fol- 

 lowed by Bronn, and practically also by Goldfuss, who, while de- 

 fining the genus as ha\dng folds both on the columella and the outer 

 Hp, places in it N. pyramidalis and N. subpyramidalis with only 

 a fold on the columella. M. d'Hombres-Firmas and M. d'Orbigny 

 have since added N. brevis, a shell without any internal fold what- 

 ever. 



M. d'Orbigny^ has given a full description of the mouth oi Neri- 

 ncea provided with an anterior and a posterior canal, and has pointed 

 out that in this genus the whorls increase rapidly in size while the 

 shell is very young, and afterwards continue of nearly the same dia- 

 meter : this gives all the species of Nerincea a certain general resem- 

 blance, by which they are easily recognised ; and it follows from 

 this peculiarity that the old shells are nearly cylindrical when the 

 columella is solid, and that in the species of pyramidal form the in- 

 crease in diameter is obtained by leaving a conical umbihcus down the 

 columella. 



The remarkable thickening of the internal folds in the upper part 

 of the shell has been frequently noticed : in some species the animal 

 continued to add calcareous matter to these folds till they nearly 

 filled the upper whorls, which then appear to have been abandoned 

 and perhaps to have decayed and worn ofP; among the larger cylin- 

 drical species of Nerincea we rarely find an old shell with its spire 

 perfect. 



Most of the shells which have been placed by different authors in 

 the genus Nerincea are so closely connected together, that they ob- 

 viously belong to one group, which unites the rhomboidal opening of 

 the Trochi to the two canals of the mouth of the Cerithia, thus form- 

 ing a link between those genera ; and of which the nearest living ana- 

 logue is the Cerithium telescopium, formed by De INIontfort mto the 

 genus Telescopium. Yet this group now contains shells of such dif- 

 ferent characters that it has become desirable to divide it either into 

 separate genera or sections. The species admit of arrangement in 

 four natural divisions, which may be regarded for the present as 

 subgenera, and may be defined as follows : 



Subgenus 1. Nerin^a. 



Columella with two or three folds ; outer lip with one or two folds ; 

 the folds all simple ; the columella solid or umbilicated. 



This division contains the typical umbilicated species of Defi'ance 

 and Deshayes ; but it cannot be limited to the umbilicated species 



* Paleontologie rran9aise, Terrains Cretaces, vol. ii. p. 72. 



