104 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 7, 



ornament, and of a conical or pyramidal form, with a wide umbilicus : 

 they are not numerous. 



Fig. 3 shows the section of the interior of N. grandis, Voltz, from 

 Alenquer, belonging to this group. 



Subgenus 4. PTYGMATIS'^ 



Columella either solid or umbilicated, usually with three folds ; 

 outer lip with one to three folds ; one or more of the folds of a com- 

 plex form, either dividing into two lobes, or wider towards the edge 

 than at the base. 



If we only looked to the number and position of the internal folds, 

 the species of this division would be united to the true Nerincece of the 

 first section ; but they form a very natural group, distinguished by 

 the complicated form of the folds, which, instead of being enlarged 

 by deposits of shelly matter along their base and sides, as in the 

 other three sections, were principally enlarged towards their edges : 

 in the upper whorls this enlargement of the folds was carried on to 

 such an extent that they nearly fill up the interior of the shell, and 

 leave a narrow passage of a most complicated form for the body of 

 the animal, which gives a very whimsical appearance to the sections 

 of the shells. Externally the shells are of a taper or nearly cylin- 

 drical form, with very little ornament, and the species can only be 

 distinguished conveniently by a section. 



Fig. 4 shows a section oiN. Bruntrutana, Thurm., from Alenquer, 

 to illustrate this subgenus. 



The following lists contain all the well-defined species OiiNerincea, 

 of which descriptions have been met with, arranged under their respect- 

 * From TTTvyixa, a fold or plait. 



