Vlll INTRODUCTION. 



The principal folds or teeth have definite positions and are 

 homologous throughout the group. The terminology now in 

 use is an amplification of that of Pfeiffer, 1848 (Monographic^ 

 Heliceorum, ii, p. 300). 



All teeth or lamina? upon the parietal and columellar mar- 

 gins are called lamella, whatever their shape; all within the 

 outer lip are called folds or plicce. In the following table the 

 names of the secondary, usually variable teeth, are italicized. 



C Twin lamella, parallel lamellae. ] Lamella angu- 



Upon the Angular lamella, spiral lamella. I laris and I.. 



parietal wall | Parietal lamella. | parietales. Plis 



(_ Infraparietal lamella. J supe>ieurs 



, T , f Supracolumellar lamella. ) Lamellae 



U P J Columellar lamella. } colurnel lares. 



( Subcolumellar lamella. J Spindelfalten 



wr-^- *u 

 Within the 



Sutural and Suprapalatal folds. ~) 



Upper palatal fold. j Plicae palatales 



Interpalatal folds. and Plica 



outer and basal ^ Lower palatal fold. basalis. 



Infrvpalalal folds. Gaumenfalten. 



t Basal fold. j 



A suprapalatal fold, when situated close below the suture, 

 is often called a sutural fold. 



The parietal and columellar lamella? and the lower palatal 

 fold usually are at the angles of an equilateral triangle, when 

 the said fold is not deeply immersed. This is useful in fixing 

 the identity of the plica?, not always clear in multidentate 

 forms, or those in which there has been extensive reduction 

 of teeth. 



Some authors have designated the folds within the outer 

 lip by number, 1, 2, 3, etc., from the upper downwards. This 

 serves very well for descriptive purposes, but the homologies 

 of the folds are entirely lost, since the upper one may be a 

 sutural, a suprapalatal or an upper or lower palatal. This 

 also affects the identity of the folds below the first. The 

 second fold in one species may be homologous with that called 

 first or third in another. 



TOOTH FORMULAS. Several modes of briefly stating tooth 



