MONSTROSITIES — HYPERSTROPHY. 
113 
contortii!^, the spire now showing on tlie riglit side, and leading to 
Pomphnly.r (fig. 2n2), wliich represents one of the extreme psendo- 
dextral or nltra-sinistral forms. In the series of figures illustrating 
these marvellous changes, the heart can be seen in the orthostro- 
phically sinistral Plnfsa to he towards the base of the whorl, and it is 
instructive to note the change in its position in refei’ence to the shells 
l)eing placed towards the upper or spire face of the whorl in the 
hyperstrophic individual, ami this without any change in its position 
amongst the viscera of the animal. The orifices of the reproductive 
and other organs in all these forms continue upon the left side. 
The shell of Pldiwrbis having become ])ractically dextral, or as it 
may perhaps be more con-ectly termed pseudo-dextral, as indicating 
its hjqjerstrophic origin from a shell primitivel)' sinistral, has naturally 
assumed some of the modifications especi- 
ally di.stinguishing the truly ph 5 dogenetically 
dextral shells, the right or primitively basal 
side of the aperture having by the inver- 
sion of the shell become the upper side, has 
ac([uired the characters suitable to its new 
position and become more advanced in 
growth, as the upper side usually is (see 
page 2"), fig. 31). Fischer and Bou\'ier, who 
assert that the anterior or basal part of 
the aperture in Limiura and P/ii/m is the most advanced in growth 
are incorrect in this and in the deductions 
they derive therefrom. 
The interesting specimen of Planorhis 
s^pirorhis figured, is sinistrally coiled and 
the elevated or snbdorsal position of the 
keel testifies that if the normal shell be 
considered as dextral or pseudo-dextral in 
accordance with its position upon the animal, 
we have here an actual instance of atavic 
reversion to the original direction of con- 
volution ; in fact, a reversal of the process 
by which the pseudo-dextral shell of Planm'bis has beeu arrived at. 
The rarity of what I venture to term the atavistically sinistral form 
and the comparative frequency of the dextrally spiral monstrosity 
F IG. 254 . — Planorhis spirorlns 
monst. priscuiu Taylor X 8, 
Clay pond, Gorton, Manchester, 
Collected by Mr. J. Ray Hardy, 
Showing atavistic reversion to 
the primitive sinistral direction 
of coiling, the keel indicating 
the sinistral organization of the 
animal. 
F IG. 253. — Planorhis war- 
ginatus m. cochlea Krown X 3, 
Risegate Eau, Gosherton, 
Collected by Mr. H. Wallis 
Kew, F.Z.S., 
Showing the pseudo-dextral 
shell, with the keel sub-basal, 
indicating a sinistral organiza- 
tion of the animal. 
