MONOGRAPH OF BRITISH LAND AND FRESHWATER MOLLUSCA. 169 
Sub-FAMiILy HAPLOGONA  Pilsbry. 
This group is, lke Polyplacognatha, composed of unspecialized and 
primitive types, which have in course of ages become diffused over the 
whole surface of the globe, but which now only retain their ancient domin- 
ancy in the extreme southern extensions of the great land masses of the 
earth, the great central desert region of North America, New Zealand, 
Tasmania, the southern portions of Australia, and islands of the Pacific 
Ocean, in all of which places they are comparatively free from the compe- 
tition of the more highly organized and recently evolved Helicidian groups. 
Haplogona is a new term used to define the Helicoid shells possessing 
simple and unreflected lip margins, and characterized by the mandible 
being composed of over-lapping and partially soldered lamin, or of seg- 
ments completely fused, the lines of fusion being indicated by vertical 
striation. ‘The teeth show no special peculiarities, except that the inner 
cusp is retained on the laterals, as in Pupide, and the genitalia are 
notable only for the simplicity of its arrangements, and the very low 
insertion of the spermatheca duct. 
The sub-family has been divided into two groups, based upon the absence 
or assumed presence of the caudal mucus gland, the genera Hndodontu 
and Pyramidula belonging to the former group. 
GENUS PYRAMIDULA Fitzinger, 1833. 
Following Dr. Pilsbry, the term Pyrumidulw is used in preference to 
Patula of Held and other names, all of which it antedates. This group, 
which embraces P. rotundata, alternata, etc., consists of dull-coloured, 
ground-loving snails, which are diffused over the whole north temperate 
land area. Its nearest relatives are Charopa, Trachycystis and Stephanoda, 
which occupy the south temperate regions of Australia, Africa, and South 
America respectively. 
All these genera may be regarded as the scattered remnants of an early 
fauna, partially dispossessed in some regions where they were formerly 
dominant by the higher and more recently-evolved groups. 
The ANIMAL shows an undivided soLr, and very long and_ slender 
OMMATOPHORES ; the GENITALIA lack all accessory organs; the puct of the 
SPERMATHECA is very long ; the HERMAPHRODITE DUCT is also very elongate 
and strongly convoluted ; and the RETRACTOR MUSCLE is attached at. or 
near the distal end of the PENIS-SHEATH, where the VAS DEFERENS also enters. 
The JAw is arcuate, its component parts fused together, the lines of 
fusion often indicated by slightly divergent striation. 
The RADULA shows a central obscurely tricuspid tooth, the side-cusps 
being indicated by a slight sinuation ; the laterals are bicuspid, and lack 
endoconic points, differing thus from Trachycystis, Charopa, ete. ; the 
marginals with low wide basal plates, the immer portion bearing two cusps, 
the outer margin becoming multicuspid by the splitting of the cusps. 
The SHELL varies in contour from a conoidal to a flattened and disc-like 
shape, is usually opaque and unicolorous ; the WHoRLS subcylindrical or 
keeled with rib-striate sculpture, and spirally banded or flammulated ; 
the apex generally smooth. ApertTURE Iunately-rounded, with a thin and 
simple margin. 
