MONSTROSITIES — HYPERSTROPHY. 
Ill 
Planorhis is a dextral shell, others affirming it to be sinistral, 
whilst a few, including the celebrated Lamarck and Deshayes, were 
disposed to view the genus as amphidromic, some species in their 
opinion being dextral and others sinistral in character. The 
apparent anomaly is, however, ingeniously and satisfactorily ex^jlained 
by the hypothesis of hyperstrophy, which makes clear the origin 
and derivation of these puzzling shells, which are in ajipai’ent dis- 
agreement with their in- 
mates and architects, d'he 
hyperstrophic theory may 
be explained by imagining 
a homocostrophic or orthos- 
tro2)hic shell as Phi/iid, 
which is .sinistrally coiled 
and is inhabited by a siuis- 
trally organized animal, to 
have its s[)ire gradually 
shortened until the shell 
becomes discoid, owing to 
the spire siidving to the 
level of the body whorl, as 
in Plannrhis, and if the process be farther continued the sjiire pro- 
trudes at the opposite side, as in the genera Pompholy.r, Cdrlnifi'.r, 
etc., all of which are sinistrally organized animals, but by the change 
described now inhabit apparently dextral shells. 
The terms Inversion or Hyperstrophy serve to indicate this change 
by which the part originally forming the base of the shell in its normal 
or primitive position becomes the nipper or spire fiice and vice rersd, 
this process also apparently reversing the direction of the coiling of 
the shell, although this reversal is arrived at in a totally different way 
and does not affect the disposition of the organs of the animal, as 
does a simple reversal of the coihng, which always involves the trans- 
position of the various organs of the body, those organs normally 
])laced on the right side of the animal being transferred to the left 
side, and vice versa. Sinistrorsity or dextrorsity by inversion or 
hyi)erstrophy is therefore essentially different from sinistrorsity or 
dextrorsity arising from a .sim])le reversal in the direction of the 
convolution of the shell. In the former case, although the mode of 
coiling has been modified, the animal retains the usual arrangement 
Fig. 238. 
An orthostrophic sinistral 
shell, as P/iysn, showing the 
heart at base of whorl. 
Fig. 239. 
Intermediate, subdiscoidal, 
sinistral form. 
Fig. 240. 
Discoid form, as Planoj'his. 
Fig. 241. 
Intermediate, subdiscoidal, 
pseiido-dextral form. 
Fig. 242. 
A hyperstrophic pseudo- 
dextral shell, as Povipholyx. 
The heart is now seen to be 
at spire side of body whorl. 
Diagrammatic figures showing in a conventional and 
simple way the change from an orthostrophic sinistral 
shell to a hyperstrophic pseudo-dextral oiie. 
