OF CONCHOLOGY. 



29 



margin of the membrane ; they are exceedingly variable in the 

 number and disposition of the denticles on their recurved apices. 



The membrane is peculiar in the small size of the recurved 

 apex of the central teeth as compared with that of the laterals. 



On plate 2 we have given a figure of one central (fig. 8), with 

 the first laterals (fig. X and 8), the second lateral (fig. 8), the 

 fifth lateral (fig. 7). The passage of the laterals into the mar- 

 ginals is shown in fig. 1. The fully developed marginals in fig. 

 2. Figure 5 gives also a form intermediate between laterals 

 and marginals. Figs. 1 and 2 are from the right of the cen- 

 tral line. The others are from the left, except fig. 8, which gives 

 teeth from both sides of the central line. 



These figures, as well as that of the jaw, are drawn from pho- 

 tographs taken directly from the microscope by our friend Mr. 

 Sam. Powel. 



ON THE LINGUAL DENTITION" OF HELICINA OCCULTA 



BY THOMAS BLAND AND W. G. BINNEY, 



In the Annals of the New York Lyceum of Natural History, 

 vol. ix, p. 287, we described and figured the lingual dentition of 

 Helicina occulta, Say. We had at* that time examined a single 

 membrane, imperfectly mounted. An opportunity has more re- 

 cently been given us to study several other membranes. This 

 has shown us that we were quite mistaken in our determination 

 of the fifth lateral tooth. It is evident that what we described 

 and figured as the fifth lateral is in reality a basal expansion of 

 the fourth lateral, belonging to the row of teeth immediately 

 above the row from which our figure is drawn. It may be that 

 this expansion forms the point of attachment of the fourth lat- 

 eral, which would account, perhaps, for the crimping of its base. 



In describing the fourth lateral, we remarked that it seemed 

 to have, in some instances, a wing-like expansion behind the un- 

 cini. This was, no doubt, the fifth lateral, imperfectly seen in 

 the lingual examined. 



The figure (fig. 6, plate 2) we have here given shows the lower 



