APERTURES IN UNIVALVES. 
33 
Oblique, when it is produced more or less 
obliquely to the axis or columella of the 
shell, as iu Helix aspersci Midler, Helix 
nemoralis L., etc. 
Fig. 74. — Example: Helix nemoralis'L.y Bitton, near Bath, collected hy Miss F. M. Hele. 
CoMPRBSSEU, when the aperture is diminished 
or compressed at the entrance, as in Azeca 
tridens (Pult.). 
Fig. 75. — Example : Azeca tridens var. noidetiana Dupuy X 3, Lewes, Sussex, collected 
by Mr. T. S. Hillman. 
Circular, when almost perfectly round, as iu 
Valvata 2^iscinaHs (Midi.). 
Fig. 70. — Example: I'alsnita fiiscinalis X 3, Graiitstown, Tipperary, collected 
by Mr. R. Rimmer, F.L.S. 
Lunate, when semi-lunar or semi-circular, as in 
Hi/(ilini(i lucidu (Drap.). 
Fig. 77. — Example : Hyali7iia lucida (Drap.) slightly enlarged, Torquay, collected by 
Mr. 13. Sturges Dodd. 
Rounded, when not perfectly round, owing to 
the interruption hy the penultimate whorl, 
as in Helix pulchelhi Miill. 
Fig. 78. — Example: Helix pulchella Miiller X 8, Kennington, Berkshire, collected by 
Mr. W. Wiiitwell, F.L.S. 
Transverse, when its greatest extension is at 
right angles to the axis, as iu Helix 
lapicida L. 
Fig. 79. — Example: Helix lapicida L , St. Vincent Rocks, Clifton, near Bristol, collected 
by Mr. J. W. Cundall. 
Pyriform, when the aperture is pear-shaped iu 
outline, the compressed portion formed hy 
the posterior sinus and the swollen part 
being at the anterior end, as in most species 
of the genus Cldusilia. 
Fig. 80. — Exatiiple : Claitsilia laitiinata (Mont.) X 2, Win- 
chester, Hampshire, collected by Mr. J. R. Brockton 
Tomlin, B.A. 
C 
