510 Mr. D. Sharp and Mr. F. Muir on the Comparative 
Sagola sp. (Pl. LII fig. 59). 
Median lobe long, slender, tubular and slightly curved, the 
median orifice at apex, the ventral edge projecting beyond the 
dorsal. Lateral lobes large, flattened laterally and lying on each 
side of median lobe, with their base in intimate union with the 
base of the median lobe. The piece we call basal-piece (bp) 
appears to belong to the lateral lobes and not to be a true basal- 
piece, but this point is obscure. Internal sac undifferentiated. 
Trichonyx suleicollis. 
Median lobe bulbous with circular, membranous patch on dorsal 
face; median orifice at distal end, closed by a chitin plate which is 
attached at the base of the internal sac; this plate moves when the 
sac is evaginated ; median foramen small, about two-thirds from 
base. Lateral lobes short, flattened, applied closely to the ventral 
face of the distal end of the median lobe. Internal sac large, 
armed with strong chitinous plates. 
Bryaxis impressa (Pl. LXXVII figs. 230, 230a and 0). 
This appears to be much on the same plan as Sugola, but the lateral 
lobes in their basal part are consolidated to the sides of the median 
lobe, and their more median portions apparently meet, while their 
outer portions remain free, divergent and pointed. If a section be 
taken through the middle of the aedeagus it should include three 
lumens, in the middle that of the median lobe (d of fig. 230b) and 
another on each side, c, the lumen of the lateral lobe. Internal sac 
undifferentiated. There is considerable difficulty in the interpre- 
tation and delineation of this structure, as regards the distal portions 
of the median strips of the lateral lobe. In the figures 230 and 230a 
it is assumed that they pass beyond the median orifice and then 
meet at the point a. 
Bryaxis guncorum. 
The aedeagus is on the same plan as B. impressa, but is shorter 
and more bulbous; the lateral lobes are consolidated to the median 
lobe. 
Physa inflata (Pl. LI fig. 58). 
Median lobe bulbous, ventral and dorsal walls chitinous with a 
membranous band (m) around the middle, median foramen small, 
ventral and nearly median. The lateral lobes hard to distinguish 
from median lobe but appear to be the two pointed sclerites on 
each side of median orifice (I), but it is possible that the median 
sclerite (a) on the ventral distal part of the median lobe represents 
