5 



convenience, the names of these ancestral-geographical groups 

 might be used in a generic sense, if only we could cease to apply 

 the name Helix to the whole of them. 



Considering the above circumstances, I propose to use the 

 generic and subgeneric divisions which have been formed under 

 Helix as Sections only, and those sections which have certain 

 common relationships as composing Groups, the latter as well 

 as the former, although in a larger sense, indicating common 

 ancestry and distribution. In a general way these groups will 

 advance from those in which the characters most resemble the 

 Zonitidae towards what has been usually accepted as the typical 

 or ideal Helix, and thence towards the next-coming genus 

 Bulimus. As I have stated that the characters distinguishing 

 these sections and groups have but little systematic value, it will 

 be readily understood that they are not readily expressible ; 

 hence no useful S3~nopsis or comparative table of them is possible, 

 and I shall simply take them up in succession in proceeding 

 immediately with the descriptions of the species. 



Group 1. SAGDA, Beck, 183?. 



Shell subperforate, or im perforate, globosely conoidal or de- 

 pressed, diaphanous; whorls narrow, aperture with interior 

 revolving lamellae, peristome simple, sharp. Jaw oxygnathus. 



Jamaica. 

 Section SAGDA (sensu stricto). 



Shell subimperforate, globosely conoidal ; spire more or less 

 elevated, with obtuse apex ; eight or nine narrow whorls, the last 

 flattened at the base, excavated around the umbilical region ; 

 with internal revolving lamellae ; columella short, oblique, dilated 

 at the base ; aperture obliquely semilunar, peristome simple. 

 Epistyla, Swainson, 1840, is a synonym. 



Section HYALOSAGDA, Albers, 1860. 



Shell scarcely perforated, depressed, hyaline, thin; whorls 

 5-7, narrow, the last excavated at the base ; aperture obliquely 

 lunar (with or without a basal lamella); peristome acute, colu- 

 mellar margin scarcely dilated, slightly reflexed, more depressed, 

 but with the same narrow whorls as in the typical section ; most 

 of the species have no internal lamella. 



