The present volume is devoted to those families of the suborder 

 Rhipidoglossa which have not already been included in the MANUAL. 

 The sequence in which the families of this group have been mono- 

 graphed, is, owing to causes not controlable by the writer, not entirely 

 natural ; a better arrangement is given in the appendix. 



The terms used in descriptions are the same as in the previous 

 volume : spiral indicating a direction parallel to the volutions, 

 longitudinal meaning parallel to the axis of the shell. The writer 

 is aware that some authors have given these terms a different sig- 

 nification ; making longitudinal a synonym of spiral, and substi- 

 tuting transverse for sculpture parallel to the shell-axis ; But the 

 word transverse has also been used by A. Adams and others, in. a 

 sense synonymous with spiral. The words longitudinal and trans- 

 verse have thus come to mean " all things to all men." Disclaiming 

 any intention or desire to criticize the usage of other malacologists, 

 the writer has adopted the nomenclature preferred by a majority of 

 English and continental authors ; merely noting in this place the 

 diametrically opposed senses in which authors have employed these 

 descriptive terms. H. A. P. 



Philadelphia, April, 1890. 



