92 THE NAUTILUS. 



The following geuera belong to the Helicoid group Haplogona.- 

 They have a shell with simple, nou-reflexed lip, more or less similar 

 to our " Patula " alternata, etc. The genital system lacks all appen- 

 dages. The foot has on each side a border above the margin bounded 

 by a groove (easily seen in alternata, solitaria, etc.). This last char- 

 acter is shared with the family Zonitidce. The jaw exhibits consid- 

 erable variety in the several genera. It is either (1) composed of 

 separate squai'ish plates, overlapping or imbricating, and only con- 

 nected by a common membrane (Punctum, Laovia'), or (2) the plates 

 are soldered together, the outer edge of each being free (FlammuUna, 

 Charopa), or (3) the plates are completely soldered together, their 

 edges appearing only as vertical strise (Pyramidula--=^" Patula"). 

 The first type has been called Goniognathous, but falsely, as it has no 

 near relationship to the jaw of Orthalicns, etc.; the second type has 

 been called Stegognathous or " plaited " ; and the third Aulacogna- 

 thous or " striated. " The three are really only stages of develop- 

 ment, and between the last two all intermediate forms occur. 



The principal peculiarity of the generative system, besides its 

 simplicity, is the very low insertion of the spermatheca duct. The 

 teeth show no very characteristic features, except that in many 

 cases the inner cusp is retained on the laterals, as in the Pupidce. 



The genera of Hajjlogona may be briefly tabulated thus: 

 a. Jaw composed of separate plates, Punctum, Laomo. 



aa. Plates of jaw more or less soldered together, 



b. Tail having a mucous pore, Flammnlina. 



bb. No mucous pore 



c. Australo-Polynesian forms, Endodonta. 



cc. S. American forms, Amphidoxa. 



cce. S. African forms, Phasis. 



cccc. North temperate forms, Pijramidnla. 



The five last named geuera include a great number Df subgenera 

 and "sections," all of Avhich are defined and fully. illustrated both 

 as to shells and anatomy, with lists of the species of each. 



The group Haplogona as a whole may be regarded as an ancient 

 and unspecialized type, formerly w^orld wide in distribution. At 

 present a vast majority of the species retain their footing only on the 

 southern extremes of the three gieat land masses of the globe, and 



-The genus Polygyra, fonneily included in the Haplogona, does not belong there. 

 It has a solid, ribbed jaw a"d no ^r jives above the fcot nirrgin. 



