8-2 
APERTURES IN UNIVALVES. 
and is then tenned “ intevnipted”; this separ- 
ation is, however, only apparent, as the wliorl 
is in all cases a complete tube, the pen- 
nltiinate whorl not forming the inner wall of 
the aperture, as has often been stated, 
in^i^i^upt^^Peristome."'' but merely the foundation or support for the 
^sV^uniTwrvorks.’, iiiiier portion of tlie last formed wliorl, thus 
E.L.s. enabling' it to liave the tlunness and delicacy 
which usually characterizes it and has caused its e.vistence to 
lie overlooked or ignored. The left side which is so often closely 
appressed and adherent to the preceding whorl, is called the 
Inner or Oulumellar Lip, and also the Labium. Pfeiffer terms 
the portion of the aperture supported hy tlie penultimate volution 
tlie Parietal Wall. 
The Palatal Lip, Outer Lip, or Labrum, is the right side of the 
_ aiierture in de.xtral shells and is usually thin and 
{ sharp in immature shells (p. 81 , f fiS); but in .some 
^ y genera, as niialhiid, it remains so in full-grown 
I'lc^. 71. — UnivMve .siieciineiis, but generally it is thickened, e.\- 
willi Siln])lc Peristome. t ft i* t l i i 
/«</</,! (I trap)., paiided, or develops tectli-like tolils, and other 
Torquay. . ■ / t- 
Coll, by .Mr. 11. s. DotUb proiiiiiieiices at maturity (j). 81, figs. Ol!, (i;)). 
d'he Aperture has its length parallel with the 
length of the shell, and its width transversely to 
this ; its many moditications in form and character 
may usually he ranged under one or other of the 
following he-i Is, and is considereil to be 
Longitudinal, when its length is iiarallel to or 
coincident with the a.xis of the shell, as in 
.'tfiujiKtlh (L.). 
I' lc.. 7*2. — K.vainple : Lhnna'a sta^s^nalls (L.), Vartlley Chase, Northamptonshire, collected 
by Mr. Lionel K. Adams, B.A. 
Aurieorm, or Auriculate, when the aperture 
has ajipro.ximately the shape or outline of 
the human ear, as in many species of 
Lhniuvhiw. 
Fig. 73. — E.vample : Livinwa nuricularia var. nlhida Jeffr., near London, collected hy 
the late Mr. J. Pickering. 
