PLECTOTROPIS TROPIFERA. 205 
SuB-FAMILY BELOGONA Pilsbry. 
The Belogona are the most highly developed of the /elicide, and have 
acquired accessory organs to the reproductive system not previously 
possessed by the family ; these consist of one or more muscular sacs or 
diverticula developed upon the atrium, within which one or more vy variously - 
shaped calcareous spicula are secreted, and in connection with these organs 
a series of glandular bodies or mucus glands are present. ‘The group is 
divided into two sections: Belogona Euadenia and Belogona Siphonadenia. 
BELOGONA EUADENIA Pilsbry. 
The Euadeniate section is the more primitive of the two groups, and 
usually possesses, in addition to the organs of the Hpiphallogona, a simple 
dart apparatus with sacculate mucus elands inserted on the dart sac or 
arising from its base. It attains its greatest development in Eastern Asia, 
the Helicostyla, perhaps the earliest member of the section with their 
primitive dart apparatus, pressing upon and overlapping the area inhabited 
by their Epiphallophorous predecessors; the group, however, still lingers in 
the European region, as one undoubted member—the Eulota fruticum— 
is found in Central and Eastern Europe, the solitary representative of 
this former dominant race. 
Though this group is now a waning one in the Old World, it is the 
most advanced and dominant group in America, having invaded that 
country by means of Behring Bridge, and spread southwards, pressing 
upon the rear of the Hpiphallogona which preceded them, and_ being 
prevented by the Rocky Mountains from effective eastward extension. 
The species found fossilized in the Oligocene and other deposits of this 
country are here regarded as Euadeniate on account of their similarity to 
recent Euadeniate species. 
GENUS PLECTOTROPIS Martens. 
Plectotropis tropifera (Edwards). 
Helix tropifera Edwards, Mon. Eoc. Moll., 1852, p. 64, pl. x., ff. 3 a-e. 
SHELL orbicular, about equally convex above and below, SPIRE slightly ele- 
vated ; WHORLS five or six, almost flat and somewhat compressed at the periphery, 
forming a sharp keel ; the under-side is tumidly convex, and shows a deep and 
moderately wide UMBILICUS margined by an obtusely- angled bend. APERTURE 
transversely lenticular, with a slightly reflected peristome. 
Diam. 125 mill. ; alt. 5 mill. 
wie \oes 
Fic. 261.—Plectotropis tropifera, showing upper, frontal, and basal aspects (after Edwards). 
Mr. Edwards compares this with /7. lapicidw, but the umbilicus is 
smaller in proportion, the keel more prominent, and the aperture does not 
show the deflection at maturity which characterizes /7. lapicida. 
Mr. Gardner thinks the Hl. coqguandiana Mathéron, from the Palzeo- 
therium limestone of Aude, France, identical with this species, which in 
size and contour he compares with //. trichotropis Pfr., a native of China. 
Oligocene—Recorded by Edwards from the Bembridge limestone, Sconce, Isle 
of Wight. Mr. C. Ashford gives Bembridge, Hempstead, Whiteclitf Bay, etc., as 
additional localities. 
