MONSTROSITIES — ABNORMAL GROWTHS. 
121 
size of the shell. Irregularity in food supply, due to the recurrence 
of alternating periods of enforced abstinence, owing to food scarcity, 
followed by terms during which ample supplies of nourishing and 
palatable food are easily obtainable, may be supposed to conduce to 
similar growths. 
An Abnormal Continuation or prolongation of the regular growth 
is occasionally made after the normal completion of the shell and 
the formation of the lip, but in nearly all 
these cases, owing to the glands of the 
collar becoming' atrophied at the maturity 
of the .shell, these extraordinary and abnor- 
mal growths are exclusively secreted by 
the visceral mantle, and are therefore quite 
destitute of epidermis and of the middle 
calcareous layer with which the coloring 
matter is usually associated, having exactly 
the same character and appearance as the 
repairs made to damaged parts of the 
shell, remote from the aperture and 
beyond the reach of the collar ; snch 
repairs are made solely by the visceral 
mantle. These abnormal growths are 
probably only another mode in which 
■ 1 1. f , 1 1 1 T f r* 1 1 Showing abnormal continuation 
tlie resiiit oi tlie prolonged lile oi tlie of growth, 
animal may be manifested, and in all likelihood this assumed pro- 
tracted life’s cycle of the mollusk is owing to unusual mildness of the 
seasons. The locality where the specimens figured and others also 
have been obtained is very suggestive, the neighbourhood being noted 
for its genial and mild climate. 
In some rare instances it may happen that the aperture is formed 
prematurely, and normal growth be afterwards continued for a short 
distance, and a new apertural margin formed, or it may be that in 
some cases the atrophy of the glands of the collar may be delayed 
longer than is usually the case. 
Anomalous Combination Shells are those formed by the union of 
two or more diverse shells, either owing to the circumstances producing 
them occurring naturally, or through artificially bringing the desired 
shells into the necessary close conjunction with each other, so that 
Fig. 'I'lX.-Clausilia bidcntata 
(Strom) X 2 , 
Cheltenham, 
Collected by Mr. W. Nelson, 
Showing abnormal continua- 
tion of growth. 
