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H 
MONOGRAPH OF BRITISH LAND AND FRESITIWATER MOLLUSCA. 133 
GENUS ZONITOIDES Lelimann. 
Zonitoides excavatus (Bean). 
18380 Helix excavata Bean, Trans. N.H. Soe. Northumb., i., p. 38. 
18380 — nitida var. a Jeffreys, Linn. 'Trans., xvi., pp. 899 and 511 
1857 — Jucida var., Turton’s Man., p. 175, pl. xii., f. 138. 
1840 Zonites excavatus Gray’s 'Turton’s Manual, p. 57, pl. iv., f. 39. 
71 Hyalina (Buhyalina) excavata Wobelt, Catal. Eur. Binnenconeh, p. 5 
1877 Hyalinia excavata Westerlund, Faun. Eur, Extram., p. 26. 
1891 Titrea (Zonitoides) excavata Smith, Journ. of Conch., vi., p. 339. 
RAusrory. —Zonitoides ercavatus (exca- 
vata, hollowed out) is one of the few 
species ane detected in the British Isles, 
and as yet has only been found in few 
localities beyond our limits, although this may 
really be due to a lack of co-ordination in 
the British and continental knowledge. 
This species is dedicated to its discoverer 
and describer, Alderman William Bean, of 
Scarborough, who by lis exceptionally keen 
perceptive and discriminatory powers dlis- 
covered many additions to the British mol- 
lusean fauna. 
The genus Zonitoides was established by 
Dr. Lehmann, of Stettin, for the reception 
of Hyalinia nitida, which he demonstrated 
to differ from the rest of the European 
Hyaliniw in possessing a_ well-developed 
dart-sac, containing a simple curved cal- 
’ Wy careous dart. 
Llc. pee he group is further characterized by its 
depressed or subdiscoidal, widely umbilicated sueLt with obliquely lunate 
aperture. 
INTERNALLY, the Jaw is broadly crescentic with rounded ends, the lower 
or cutting margin with a noticeable protuberance or beak, and the upper 
margin bearing a somewhat corresponding depression. 
The REPRODUCTIVE ORGANS show several primitive characteristics, which 
are paralleled by similar structures amongst the peculiar genera inhabiting 
the Malayan region. 
They possess a STYLOPHORE or dart-sac, bearing near the distal end a 
conspicuous projecting gland, named by Dr. Pilsbr y the CORONAL GLAND, 
which in the far east 1s represented in certain species by a circlet of 
glands encircling the sac; the DART is a simple, curved, and slightly- 
twisted crystalline weapon, which, though exactly analogous to the 
Helicine dart, is not regarded as its homologue, but as a distinet strue- 
ture, and has, therefore, been named Pugio by von Ihering to emphasize 
its independent origin in this group. 
A further peculiarity is the bifurcate stem to the SPERMATHECA DUCT, 
one branch debouching at the bare of the FREE ovipucT and the other 
into a cul-de-sac surrounding the PENIS, ete. 
One of the most remarkable structures in the group is the peculiar 
calcareous CHANNELED PLATE within the penis sheath, quite analogous to 
that found in Cochlicellu acuta, and whose function is as yet quite unknown, 
