212 On the Oral Folds in the Shells o/Clausilia. 



Clessin (1876) * omitted these, and introduced some slightly 

 different vernacular names for certain of the others. 



Schmidt's system was followed by Bottger (1877) f, who 

 slightly modified (as noted in the table) the method of enume- 

 rating the plicce palatales. To this modified scheme Wester- 

 lund and Von Mollendorff have given their adhesion, and it 

 is the one adopted in the first column of the table as being the 

 fullest and most satisfactory. 



Kobelt (1878) {, like Clessin, omitted to mention the folds 

 described by Schmidt in 1S68, and, in addition, restricted the 

 term " Gaumenfalte " to the plicce palatales. 



Fischer, in his Manual (1881, pp. 484, 485), gave some 

 useful figures ; but, as already noted, his nomenclature is 

 imperfect, the work of his German contemporaries being 

 overlooked. 



Finally, Von Martens (1883) § gave a figure with the ver- 

 nacular names of the principal folds, but, strange to say, 

 made no reference to those on the columellar wall. 



It may be as well to draw attention to the fact that those 

 plaits which occur on the columella itself and on the colu- 

 mellar wall above are called " lamellaj," whilst, on the other 

 hand, those only which are met with on the outer wall of the 

 body- whorl are designated " plica?." If this application of 

 the terms plicce and lamellce be universally adopted a good 

 deal of misapprehension and confusion will be avoided. 



As regards the meaning and origin of these curious depo- 

 sitions — for they are such, and not in any strict sense folds — 

 the present is not the time or place to enter into any specu- 

 lations ; but the following points deserve attention : — 



1. The lunella is sometimes replaced by a series of very 

 short plica? ranging one above the other in such a manner as 

 to suggest the very strong probability that this fold arose 

 from their coalescence. 



2. In the same way the lamella fulcrans would seem to 

 result from a thickening of part of the I. spiralis, which blends 

 with the similarly thickened /. inserta, till they spread across 

 to the neighbouring folds ; for when /. fulcrans is present 

 I. spiralis and /. inserta are so reduced as to be scarcely 

 perceptible if they be not altogether lost. 



It must be understood that the figures here siven are more 



* Deutseh. Excur. Moll. Fauna, p. 227. 



t ' Clausilienstudien. — Palaeontographica,' Supp. iii. p. 10. 



X ' Illustrirtes Conchilienbucb,' p. 285. 



§ ' Die Weich u. Sclialthiere,' pp. 136-138. 



