ThevH'1l $s fT OR Y¥ 
Of the umbilicated marble Snail, 
This little Snail, which is variegated in the 
manner of marble, inhabits the frefh-water 
rivers of Holland, and therein adheres to {mall 
ftones: I have found it in the Vecht, beyond 
Amfterdam. It is frequently found about pieces 
of brick-bats and tiles, or pot-fherds, broken 
pieces whereof have been thrown into the 
water. In the fore part, where the fhell ga- 
thers into a {piral form, fig. 11. a, it refembles 
an umbilicus or navel; then it bends or rolls 
round in an oval winding, and becomes more 
expanded 4. It is of a green yellow colour, 
variegated with a reticulated black ground like 
marble. The Snail that lives within is very 
tender, and as it died before I had brought it 
home and opened it, I cannot fay much con- 
cerning it, nor exhibit the figure of its body. 
I faw that it had two oblong and fharp horns, 
and two black eyes. The ftructure of its 
tongue is almoft the fame with that of the won- 
derful Snail. It had pretty ftrong little intef- 
tines. Its body, which was contained within 
the extreme fpiral part of its fhell, was of an 
obtufe figure; becaufe, probably, this fhell was 
very thick, firm, and folid. To the lower part 
of the body adhered a calcarious operculum or 
cover, which had a kind of fwelling or pecu- 
liar production where the mufcles were in- 
ferted into it, fo that it refembles the thoulder- 
blade in the human fkeleton. On the outfide 
it was twifted fpirally like the fhell itfelfi On 
the inner part, where this Snail creeps out of 
its fhell, the opening or entrance, which is 
formed like a crefcent, only was open, and 
over-againtt it I obferved a certain greenith {pot, 
which refembled in fubftance the thell of mo- 
ther-of-pearl, and was likewife of the figure of 
a crefcent. To this fpot the operculum or 
cover applies itfelf, when the Snail creeps out 
of its fhell. 
The flattened Snail. 
Since many fpecies of Snails are found in the 
rivers of our part of Holland, I thall briefly 
defcribe only one kind of the water race, which 
is to be found there very common, both in 
falt and frefh water, as alfo in pafture grounds 
and near the high-ways. Its body is gray or 
blackifh. On or at the fore part of the head 
are obferved two lips, Tab. X. RiGee I, 22 
joined together, under which is the Snail’s 
mouth, formed in the fame manner as it is in 
the common water Snail. Under the mouth 
there is to be obferved a part of the body, 
which I call the verge or foot 44, becaufe it 
ferves it to creep with, The Snail frequently 
expands this verge in fuch a manner as to cover 
the lower part of its lips and mouth there- 
with. A little higher in the head are two 
black eyes cc, fituated at the bafis dd of the 
horns. ‘Thefe horns are very fharp in the fore 
_ part, but broader behind, and the Snail can 
ef eS GaGa wT 1S) 83 
contract them in fome degree, but it cannot 
abfolutely draw them back into the body. 
When its body e is puthed forward out of 
the fhell, it is confiderably long and flender. 
Near the fhell is obferved a part of the verge, 
which the creature can‘raife out .of the water 
when it {wims; fo that by means thereof, it 
may draw the air into its body; the verge 
therefore has for this purpofe a fufficiently 
large aperture, Tab. X. fig. 111. f; in’which | 
is {een the openings g defigned for the organs 
of generation. 
Its thell or hard skin is twifted or rolled about 
in a wonderful manner, and on the left fide it 
is {mooth or flat hb. It is invefted with a di- 
ftinétly vifible periofteum, and is divided by 
very {mall incifions, ribs and furrows. Bat if 
this fhell was fo foft as that it could be rolled 
out, an oblong tube might be made of it. On 
the right fide it is concave or diverging as it 
were from itfelf, but on the infide it is rolled 
into itfelffig. 1v.a, and therefore leaves a {mall 
aperture in the middle, which I call the cavity 
of the pillar. 
This Snail is a kind of intermediate f{pe- 
cies between the common water and viviparous 
Snail, as will appear from its diffeCtion now to 
be exhibited. It is very difficult to diffect it, 
for it cannot be killed without hurting it, and 
it will not admit of being diffected alive. How- 
ever, I do not doubt but I may be able to 
furmount this difficulty, by the invention of 
fome proper apparatus for that purpofe, which 
I the more ardently with for, becaufe as foon 
as one begins to break open the fhell of this 
Snail, it immediately difcharges a purple fluid 
or humour, which diffufes itfelf throughout the 
infide ; even through the vifcera. If you kill it 
in fpirit of wine, it likewife expels this pur- 
ple fluid out of its body; but when it dies na- 
turally in a little water, it fhews no purple, be- 
caufe the colour then probably vaniihes by the 
changing the difpofition of the parts. When 
this Snail is drowned in milk, in which how- 
ever it will live for fome time, it is notwith- 
ftanding found that the purple humour does not 
remain in the veflels appropriated to it by na- 
ture: and though I faw the heart beating, 
yet I never found this purple liquid in it or its 
auricle. Hence I am inclined to think, that 
this liquor is contained in a kind of facculus or 
bag, which I have feen in other Snails, but 
could not hitherto difcover in this. 
The thell being gradually and carefully broken 
off from the body, the diffection thould com- 
mence from the aperture of the verge. It will 
then appear, that this Snail agrees greatly with 
the wonderful {pecies ; for the verge is likewife 
here provided with a fimilar {mall margin beau- 
tifully folded, and made in the fame manner as 
in the Snail before-mentioned ; for in its texture 
is likewfe found a very great number of fuch 
chryftalline globules, which crafh and make a 
noife under the inflruments. On the other, that is 
on the right fide of the verge, is alfo obferved 
a congeries of fuch Worms, as I have in like 
Manner 
