8 Descriptions of new species of Diplommatina. [No. 1, 



or less blunt tooth-like process, characteristic of the genus. 

 Situated also at the constriction on the roof of the whorl at this 

 point may be seen a long tube-like ridge, very similar to the 

 external tube of Alycaus, only that it diminishes from the back 

 forwards. The position of the operculum as regards both this and 

 the lower rim is at the back. It does not seem to me at all clear, 

 for what purposes this internal formation has been created. 

 Possibly the extremity of the foot carrying the operculum travels 

 along the screw-like thread, and the ridge above may give the 

 necessary guiding surface to the operculum when the animal 

 issues from its shell. The operculum, situated as it is so far from 

 the aperture, would require some fulcrum or guiding edges, to pass 

 it evenly and smoothly out of the shell. 



On plate ii, in figure 3, I have endeavoured to shew the position 

 of the operculum and constriction from the front of Dipl. paclnj- 

 clicilus ; in fig. 4, the interior of the shell from the left hand side, 

 where t represents the spiral rim ; c, the position of the constriction ; 

 r, the upper ridge or tube. 



Figs. 5 and 5a, are respectively a side view and plan of the 

 relative positions of the operculum and the commencement of the 

 spiral rim. 



In fig. la, pi, I, I have shewn the position of the constriction in 

 D. Jatingana, situated behind the aperture, a considerable distance, 

 and as yet peculiar to this species alone. 



Fig. 6 is the lingual ribbon of D, pacliychcilus, B s., — the outer 

 laterals are very small and indistinct. 



In order to compare the lingual ribbon of Diplommatina with 

 those of other allied genera, I have added figures of the dentition 

 of an Alycceus and of a Pupina. (vide fig, 7 and 8, pi. II). 



Fig. 7, is taken frorn a large form closely allied, or identical with 

 A. Ingrami, Bens.; fig. 8 represents the dentition of P. imbricifera, 

 Benson. 



In Alycceus the form of arrangement is z f T T T fj, all the uncini 

 being 5 cusped, with the exception of the outer on which I could only 

 detect 4. It may be noticed that in the drawing the 5 cusps are not 

 shewn in every instance, but it must be remembered that they can 

 only thus be seen in certain positions, or from certain points of view 



