120 
MONSTKOSITIES — POLYl’EHISTOMATISM. 
PuLYPEHij'TOMATE (ttoAi's, iiiuiiy ; irtpi, aruuiul ; and o-ro/xa, mouth) 
would perhaps be a more correct designation for certain shells, which 
though differing somewhat from the tridy distoinate shells, are 
yet eipially interesting, and of which the Limnau peregm 
discovered by l\Ir. William Nelson in 
the spring of 1883 in a small shallow 
cattle pond at Allerton - Bywater, near 
Leeds, are a remarkable illustration. 
These shells, and all in the pond were 
more or less affected, are somewhat 
irregularly and often fantastically grown, 
and in addition to thismalformed growth, 
sometimes developed two or more complete peristomes or lips to 
tlieir shells ; these lips, though more or less coiiHuent and grown 
together at the imsterior margin of tlie shell, become (juite distinct 
and separate at the anterior or basal portion, and the complete shells 
have in some cases all the appearance of one or more distinct shells 
enclosed within a larger e.xternal one. 
Tlie I’elecypods also occasionally e.xhibit this duplication of the 
apertural margin, and characteristic specimens i)resent, as in the 
Fig. 2G0. — L. pcrc^ra (Miill.) X 2, 
PoikI, Allerton-Pywaler, Vorks., 
Collected by Mr. W. Nelson, 
Showing three diblincland separate 
peristomes. 
Fig. 270. — i'nio iionitius Phil., 
(irohy Pool, Leicestershire, collected by Mr. H. K. (Juilter, 
Showing the formation of three distinct and successive peristomes. 
I A mini <1 jn rrgra above mentioned, all the ai)pearance of several shells 
enclosed within an outer larger one, and in an even more deceptive 
manner. 
These additional lips are usually of less anii)litude at their origin 
than the one previously made, and have been noted to be often hjrnied 
in spring, when the emaciation or reduction in bulk of the body which 
may be assumed to take i)lace during hibernation has not heen fully 
compensated for before the growth season has recommenced and this 
diminisheil size of the body would necessitate a contraction in the 
