feme minute Britifh Shells . 163 
But I mufl not conclude my remarks without taking fome 
notice of the Inhabitant of this Angular fhell. It appears to 
be of the fug kind, but differs from the common land forts in 
this refpedl, that the Antennae are filiform , and the eyes not 
placed upon their fummits and retractile , but fixed upon the head 
near their bafes, as is probably the cafe in all the truly aquatic 
kinds, at leaft in all fuch as I have hitherto examined. The 
animal is of a foft and flexible nature, and grey brown co- 
lour, and has a power of extending itfelf out of the fhell 
through the aperture of the exterior feptum ; at which time it 
affumes a triradriated fhape, not very diffimilar from the aper- 
ture itfelf, or like an inverted Y QQ, the thickeft ray of which 
is the head and body ; one of the lines which form the angle 
is the tail, and the other is a kind of dorfal ligament, which 
extends from the back of the animal, through one of the rays 
of the aperture, and through the whole cavity of the fhell, 
and all its fiepta , to the centre, as may be feen by placing the 
fhell between the eye and the light (fee fig. 3. Tab. I.). 
In the concife Linnjean mode of defeription this fhell 
may be named, 
Nautilus ( lacufiris ) tefta fpirali comprefla umbilicata cari- 
nata, anfraftibus tribus fupra convexis contiguis, aper- 
tura femiovata, feptis triradiato-perforatis. 
The Frefh- water Nautilus. 
I find no author who has taken any notice of this fhell, ex- 
cept Mr. Walker, who, in his late curious publication on 
Minute Shells , has deferibed it under the name of 
Helix hneata dorfo convexo umbilicata margine acuto ; and 
has given a figure of it in the fame wofk, PI. I. fig. 28. 
But this ingenious gentleman is free enough to confefs, 
that its chambered firullure had entirely efcaped his notice,. 
Y 2 otherwife 
