™, 
208 MONOGRAPH OF BRITISH LAND AND FRESHWATER MOLLUSCA. 
BELOGONA SIPHONADENTIA Pilsbry. 
his group, which is especially characteristic of the European region, 
is more advanced in organization than the Huadenia from which they have 
arisen, and contains the most highly-developed Helices known, comparing 
with the white man in their comparative superiority over other races, 
and possessing the same ability to colonize and dispossess the original 
occupants of other lands. 
In the Siphonadenia the dart apparatus of the Euadeniate species has 
become more perfected, and the sacculate mucus glands have been removed 
from the dart-sac to a higher position on the free oviduct, and become 
elongate and of equal diameter throughout or digitate in character, all 
peculiarities which culminate in the group Pentatenia, of which Helix 
nemoralis, H. aspersa, etc., are typical, and which represent the most 
highly organized Helices in the world. 
The less-advanced and degenerate species may exhibit the dart apparatus 
and mucus glands in a more or less comparatively vestigial condition, and 
one or both of these organs may even be quite lost, thus reverting in these 
respects to the earlier and more primitive condition characterizing their 
predecessors, the Kpiphallogona ; the true position of such species is 
determinable only by a study of their developmental history or by the 
examination of the organization of allied species in which the various 
stages of the degeneration can be traced and confirmed. 
Dr. Pilsbry has remarked that several recent groups, as Helicella, 
Hygromia, Cochlicella, etc., are genera which have undergone degeneration 
of certain of the organs of reproduction, resulting in the secondarily 
simplified forms by which they are characterized, and it is remarkable 
that frequently the species or groups in which these organs have retro- 
graded are those in which the penis, mandible, radula, and shell show no 
traces of degeneration, but retain the characters peculiar to the genera 
from which they are believed to be derived. 
Dr. Pilsbry is of opinion that the Belogona originated in the Kast, and 
that species with reproductive organs similar to those of the early 
Euadeniate group Helicophanta, afterwards spread westward into Europe 
before or during early Eocene time, and there became modified into the 
Siphonadeniate type, and splitting up into a considerable number of 
genera, crowded out of Europe the less-perfected early possessors of the 
soil, although he further expresses a belief in an interchange of species 
between Eastern Asia and Kurope. 
That the Siphonadeniate species have been evolved on European soil, 
and are not immigrants, can scarcely be confuted ; but it is also probable 
that no immigration from the east ever took place, or any interchange of 
species between the two extremities of the Eur-Asian tract. 
Though in its most highly developed forms this group is especially 
distinctive of the Western Palearctic or European region, yet certain of 
the earliest evolved and more simply organized Siphonadeniate species 
have penetrated eastward as far as China, and represent the advanced 
enard of the group, mingling with and pressing upon the rear of their 
Kuadeniate predecessors. 
