92 THE NAUTILUS. 
The following genera belong to the Helicoid group Haplogona.* 
They have a shell with simple, non-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 Zonitide. _ The jaw exhibits consid- 
erable variety in the several genera. It is either (1) composed of’ 
separate squarish plates, overlapping or imbricating, and only con~ 
nected by a common membrane (Punctum, Laoma), or (2) the plates 
are soldered together, the outer edge of each being free (Flammutina,. 
Charopa), or (8) the plates are completely soldered together, their 
edges appearing only as vertical strie (Pyramidula—“ Patula”’). 
The first type has been called Goniognathous, but falsely, as it has no- 
near relationship to the jaw of Orthalicus, etc.; the second type has. 
been called Stegognathous or “ plaited” ; and the third Awlacogna-- 
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 Pupide. 
The genera of Haplogona may be briefly tabulated thus: 
a. Jaw composed of separate plates, Punctum, Laoma.. 
aa. Plates of jaw more or less soldered together, 
b. Tail having a mucous pore, Flammulina.. 
bb. No mucous pore 
c. Australo-Polynesian forms, Endodonta.. 
cc. S. American forms, Amphidoxa.. 
ecc. S. African forms, Phasis.. 
ecee. North temperate forms, Pyramidula.. 
The five last named genera include a great number of subgenera 
and “sections,” all of which 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 world wide in distribution. At 
present a vast majority of the species retain their footing only on the 
southern extremes of the three great land masses of the globe, and 
*The genus /o/yeyra, formerly included in the //af/ogona, does not belong there.. 
It has a solid, ribbed jaw and no grooves above the foot margin. 
