390 PROCEEDINGS OF THE ACADEMY OF [1892. 



the case witli ancient characters, we find these features retained in 

 a number of very dissimilar genera. 



The characters and value of the jaw as a basis for classification 

 have been much misunderstood in the past, and even yet there are 

 a number of unsettled questions concerning it. On some points, 

 however, we may speak with considerable confidence. One such is 

 the fact that i/te strongly ribbed type of jaw (odontognath) inter- 

 grades by imperceptible stages with the entirely smooth, Zonites-like 

 type (oxygnath). Examples illustrative of this dictum are numer- 

 ous, the restricted section Caracolus of Eastern Cuba and Haiti 

 and the section Dentellaria being unquestionable instances of inter- 

 gradation, some species of each of these groups being typically 

 oxygnathous, others being jjronouncedly odontognathous. To 

 W. G. Binney is due the credit of first pointing out the fact and 

 insisting upon its implications. The writer has confirmed it by 

 the examination of numerous additional species. It is hardly 

 needful to say that in many groups of Helices, odontognathy and 

 oxygnathy are therefore controvertible terms, as far as classification 

 is concerned, and consequently cannot be used for the separation of 

 genera or even subgenera, unless supported by other and more 

 stable characters.* 



The jaw composed of a number of separate and similar squarish 

 plates, more or less overlapping at the outer edges (such as that of 

 Punctum'), is comparable to an unsoldered jaw of the plaited (or 

 stegognath) type. 



Primarily the Helicoids are divisible into a number of groups, as 

 follows : 



Eggs or young very large at birth (1 to h the diameter of the adult 

 shell) Group I, Macroon. 



Eggs or young smaller or minute at birth. 



a. 9 genital system having a dart sack and mucous gland. 



Group II, Belogona.^ 

 aa. 9 system lacking accessories ; S system with flagellum 

 and appendix on penis ; no epiphallus. 



Group III, Teleophalla. 



^In some species of Dentellaria the sculpture of the jaw is not even constant 

 as a specific character. 



^The terms " Haplogon " and " Belogon '" were proposed by v. Ihering, Mor- 

 phol. u. Syst. Genitalapparates Helix, i, p. 401, 402. 



