128 
AUXILIARY ORGANS — CLAUSIUM. 
/ 
Fig. 2St. — Clausium of C/ausiita 
Inwiuata (Mont.) X S, 
Cooper's Hill, Cheltenham, 
Showini; the concave internal face 
and the sinuate lower marj^in. 
tlie jialatal plications tliat may be present in the sliell, exliibits a 
coiTOspondinp; and apin’ojn'iate sinnation of its external outline, and 
is an organ certainly deserving of mnch 
more careful study than it has hitherto 
received from British conchologists. 
Uidike the opercnlum, which is at- 
tached to the animal and present from 
the earliest age, the clansium is attached 
to the shell only, ami is not present in 
the young, being only produced at the 
a])proach of maturity, the pedicle being first formed and the lamella 
gradually ailded to until completed. 
When the animal emerges from the shell, the clansium is pushed by 
the pressure of the body against the columella, into the groove between 
the inferior and suhcolumellar lamelhu, 
thus leaving the meansof exit free. On the 
withdrawal oftheanimal intothe shell the 
pressure of the body against the lamella 
is removed and the elastic pedicle causes 
the filament to spring into its normal 
])osition, with its lower margin against 
the exterior of the whorl, but when the 
shell is thus closed there still exists a 
small opening near the suture which is 
conjectured to serve for res]iiration and 
defecation. In the emi)ty shell from 
which the animal inhahitant has been 
removed and the lamella become rigid and dry, the elasticity can be 
to some extent restored by immersion in water. 
'riiough especially indicative of tbe 
fill liquid’, there is found in Azera tridmiK 
an imperfect, laidimentary and inflexible 
lamella, which is attached along its whole 
length to the columella, and has been 
assumed to rejn-esent the more elastic 
clansium. This rigid calcareous fold is 
continued (piite to the aperture of the 
shell, within which its rounded termina- 
tion may ho seen ])arallel with the columellar margin. 
Fig. 285. — Section through shell of 
Clausilia hideutatn Strom, showing 
tile dausium in sitr'i, X \ (section cut 
liy Mr. F. Rhotle.n). 
Fig. 280 . — Azcca triiii-ns (Pult.) xfi. 
Ronndh.'iy, near Feeds, 
Sliowing the uifle.xihle calcareous 
lamella, assumed to represent the 
Clansium. 
