91 
PLANORBIS obtusus, 
TAB. CXL .—Fig. 3. 
Spec. Char. Depressed, left side most concave : 
volutions embracing, slightly compressed on the 
right side ; aperture obliquely and obtusely 
ob cordate, 
The volutions are very few and much concealed, the 
obtuse rounding edge which gives the short obcordate 
form to the aperture distinguishes it from the next species ; 
its thickness is equal to about one-fourth of its width ; it 
is very pellucid and shining. 
Found in the same stone as the last. 
PLANORBIS lens. 
TAB. CXL.— Fig. 4, 
Spec. Char. Lenticular, subcarinated, volutions 
embracing; aperture very oblique, obcordate. 
Altogether much flatter than the last, with the sides 
more equally concave; about one -sixth of its width in 
thickness ; it much resembles the recent British Planorbis. 
From the Isle of Wight, with the above and following 
species. 
PLANORBIS hemistoma. 
TAB* CXL,— Fig. 6. 
Spec. Char. Depressed, smooth ; right side con- 
vex, umbilicate ; left side flat ; aperture 
oblique, subtriangular, 
A minute shell, seldom exceeding one line in diameter 
and a fourth of one in thickness : the volutions, although 
partly concealed by hanging over on the right side, make 
no impression on each other : the aperture is triangular* 
with the angles and one side rounded. 
I picked this up in sand at Plum stead along with Car- 
dium plumstediense and various other marine shells, 
Sharks’ teeth, &c. The lower figures are magnified* the 
upper figure about the natural size. 
