MONOGRAPH OF BRITISH LAND AND FRESHWATER MOLLUSCA. 77 
GENUS THEBA Risso. 
(Teba, Leach; Zenobia, Gray; Carthusiana, Kobelt ; Euomphalia, Westerlund). 
HE genus Theba has been adopted for the 
reception of Helix cantianu and H. curtusiana, 
and though these are the only constituent species 
found in the British Isles, many others occur in 
the Mediterranean region. 
‘The names 7Theba and Tebu are doubtless essen- 
tially the same, although Comm. Caziot regards 
Leach’s name as meaning a hill, and that of Risso 
as having a different signifies ition, yet the close 
association between Risso and Leach justifies the 
view, that in spite of the probably accidental 
orthographical difference, both names have the 
same significance and are presumably based upon 
the name of the ancient city of Thebes, which is 
rendered the more probable from the predilection 
of Dr. Leach for geographical, eastern, or biblical 
L Moetvond) names, with no necessary connection with the 
ee 
objects to which the names were applied, as has 
been so clearly demonstrated by the Rev. G. A. F. 
Knight, and we have in further corroboration Dr. Jeffreys’ authority for 
the statement that Risso did obtain the name Theba from Dr. Leach’s ms. 
With the present group I associate the late Dr. S. P. Woodward, one 
of the most eminent of British conchologists, aud author of the classical 
work “A Manual of Recent and Fossil Mollusea,” a work which was and 
is held in such high appreciation by the scientific world that it has run 
through several editions, and been translated into other languages, as well 
as formed the basis upon which similar works have been issued in France 
and elsewhere. In the domain of philosophical thought, he was, perhaps, 
the first or one of the first to suggest the probability of the existence of 
one chief evolutionary centre “from which the first and greatest types of 
life have emanated.” 
The genus 7Theba has a smooth, narrowly umbilicate and whitish shell, 
often faintly translucent, with faint sculpturing or delicate spiral lineation, 
and often exhibiting a pale supra-peripheral zone, analogous to and prob- 
ably homologous with that of other Helicidians, and indicating their descent 
from a distinctly banded, far distant, but common progenitor. 
INTERIORLY, the 'l'hebz possess a slightly arcuate and narrow jaw, with 
numerous flattened ribs, and with or without a slight medial rostration. 
The genitalia show the most striking peculiarities ; the penis-sheath is 
short and tumid, with a long, tapering epiphallus, a short flagellum, and 
no retractor ; the dart and dart-sacs have undergone more or less degenera- 
tion, and in some cases their original form has become lost, and their 
functions have become transferred to the new organs into which they have 
become modified. As in Ashfordia the right tentacular retractor is free 
from entanglement with the genitalia, and the seminal products are trans- 
ferred by means of an elongate and serrate spermatophore. 
The group is widely distributed in Europe and the near Kast, and is 
somewhat improbably assumed by M. Fagot to have arisen in the 'Tauric 
region, and to only live within maritime influence. 
