Discrimination of the Sexes in the Genus Paludina. 85 ° 
EXPLANATION OF PLATE X. 
The numbers placed beside the figures express the enlargement in 
diameters. 
Fg. 1. A nymph of Tricoryphus (sp.?), X 5. a, rudimentary respiratory 
organ of the first segment; the chitinous plate, 0, has been 
removed on one side to show the following respiratory organs. 
Fig. 2. Betisca obesa, seen from above and drawn from a nymphal enve- 
lope, in which the last segment and the antennze were deficient, 
x 5. 
Fig. 3. Prosopistoma punctifrons, nymphal stage, seen from above, x 12. 
The left half of the carapace has been removed to show, in front, 
the digestive tube partly concealed by the left lobe of the genital 
gland ; behind, the interior of the respiratory chamber, in which 
is the sheath of the lower wing (jf) concealing the points of 
insertion of the first two tracheo-branchie. 
Fig. 4. Prosopistoma punctifrons, nymphal stage, seen from below, x 12. 
The last segment, with the sete, has withdrawn into the ninth 
segment; at v and v' are the apertures which give the water 
access to the respiratory chamber. 
Fig. 5. One of the ova found in the body of the subimago of Prosopi- 
stoma, X 120. 
Fig. 6. One of the nodosities of this ovum, much enlarged, x 400. 
Fg. 7. Female (subimago) of Prosopistoma punctifrons, seen from above, 
x 14. The stigmatic apertures may be seen on the right side 
of the third, fourth, fifth, and sixth serments. 
Fig. 8. The same, seen from below, x 14. In order to avoid making 
this figure too complicated, I have not represented the legs of 
the second and third pairs, and I have left only the first two 
joints of those of the first pair. 
Fig. 9. Base of the inner surface of an upper wing, x 30. 
Fug. 10. Fragment of the posterior margin of the same wing, to show the 
multitude of hairs which cover both surfaces of the organs 
of flight, x 30. 
Fig. 11. Lower wing, x 18. 
Fig. 12. Right compound eye and lateral ocellus, in their respective posi- 
tion, X 80. 12q@isa hair from the integument of this region, 
much enlarged. 
Fig. 13. Antenne, x 60. 
Fig. 14. Leg of the third pair, x 50. 
Fig. 15. Ventral surface of the abdomen of the female subimago, x 35. 
Fig. 16. One of the two plates forming the ventral surface of the last 
segment, X 80. 
Fig. 17. The three setze of Prosopistoma in the perfect state, xX 80. 
N.B. In several of the figures I have not represented the villosity due 
to the presence of the hairs which cover the integuments and the wings of 
the subimago. 
VIII.—Notes on Indian Land and Freshwater Mollusks.— 
No. I. On the Discrimination of the Sexes in the Genus 
Paludina. By J. Woov-Mason, Deputy Superintendent, 
Indian Museum, Calcutta, on Special Duty in Assam. 
WHILE at Balaganj and Panchuganj, on the Kusiara river, 
in Central Sylhet, on my way to Cachar, I was struck by the 
