858 NATURAL 
Jour when alive, or fresh, and opaque yel- 
Jowish-white when dead ; and are distinguish- 
ed from any other, by the remarkable sinus in 
front, near the end, through which is a 
groove or channel; but this perforation is 
anly to be distinguished when the valves are 
faid open. Had Gmelin made any mention 
of this singular structure, we should have 
been inclined to think these were his M. lu- 
feus and M. flavidus:* buy as we have not 
at present an opportunity of consulting the 
figures of tlrose insects given in Muller, must 
leave the matter to be decided by entomolo- 
gists ; craving pardon for this digression. 
<< We cannot however quit the subject 
without remarking, that the surest distinction 
between the shells ofthe bivalve monoculi and 
the minnte bivalve testacea is, that the latter 
always, more orless, possess some concentric 
wrinkles or annulations of growth, as well as 
some appearance of umbo cr beak: such 
therefore, which are destitute of these marks, 
may with eontidence be referred to the former. 
** Ifany such doubiful objects are put into 
water, even after the animal has been long 
dead and dried; and whien softened, the 
valves carefully opened with the point of a 
fine needie, and afterwards put mto a drop of 
water under a micrescope ; the antennz and 
Jegs will soon appear, if a monoculus,” 
Eimnezus, on the authority of Hassel- 
quist, calls the animal of the pinna,a 
Imax, to which it has not the smallest 
affinity. ‘It appears more nearly allied 
to the animal of the mytilus, which is 
called by Linneus an ascidia with a 
mark of doubt. It seems to be entirely 
destitute of locomotion, being immove- 
ably fixed by its byssus to other bodies. 
The muricata of Linnzus is added to the 
two former British species.. The genus 
nautilus, the second of the Linnzan uni- 
valves, was not admitted into the British 
Zoology. A number of minute species 
have since been discovered by Walker 
and others, some known to Linneus and 
others not. Mr. Montague has given 
16 species. 
The animals of all the 12 following 
univalves are said to be a limax, but, as 
Mr. Montague observes, “ the greater 
part of them do not correspond with the 
definition of the mollusca animal. It is 
well known that most, if not all, fresh 
water, as well as most marine univalve 
"shells are inhabited by an animal possess- 
ed of only two feelers, destitute of eyes at 
their tip, but (Aaving them) placed at 
their base,varying in situation in different 
subjects. But besides this difference, the 
circumstance of the aquatic testacea, be- 
* The antenne 
several bristles, 
7 
HISTORY. 
ing inhabited by animals of different 
sexes, and not hermaphrodites, as im the 
mollusca limacis, have not been sufh- 
ciently attended to. It will be found 
also that some are viviparous, and others 
oviparous: and it is remarkable that 
all those with four tentacula, whose eyes 
are placed at the summit of the twa 
longest, are hermaphrodite, and are alk 
land species. Those with two tentacula, 
and their eyes situate on the head, are of — 
different sexes, and except two known 
species at present (turbo elegans and 
carychium) are all aquatic. 
«« That the Linnwah Timax ought to he di- 
vided there cannot be the least doubt ; but 
we cannot agree with Muller, that it is ca- 
pable of forming so many genera, by the mere 
circumstance of the eyes being placed a little 
more or less behind, or on one side of the 
tentacula. ‘There seems, however, to be two 
strong natural divisions: first, those with 
ocellated tentacula ; and second, such as have 
their eyes situated on the head: each of which 
might again be divided into two families 4 
thus, 
1 LIMAX. : 
** Body oblong, creeping, with a longttu~ 
dinal, flat disk, or sustentaculum, beneath 4 
foramen, or aperture, most usually placed on 
the right side : tentacula ocellated. 
‘« Terrestrial hermaphroditical. 
«** Tentacula four: eyes two, placed at 
the summit of the two langest. 
ss #* ‘Tentacula twa. 
2 LUBRICA. 
* Body oblong, creeping, with a Tengitu- 
dinal flat disk, or sustentaculum, beneath : 
foramen, or aperture, most usually situated 
on the right side: tentacula not ocellated :~ 
eyes two, placed on the head. Mostly aqua- 
tic, and of diferent sexes, 
«© * Tentacula, or feelers, four, one of 
which is plumose. : 
sc x* Fentacula two. 
«< To the first division of the limax would 
belong all the mollusca tribe usually termed 
slugs : of these the limax cinereus and agres- 
tis, Gmelin p. 3100, and p. $101, appear to 
be the link between the testacea and- mol- 
lusca, (being possessed of a shelly substance 
under the shield upen the back,) connecting 
these land animals together ; as some of the 
marine bull do that of the aquatic: bulla 
aperta, haliotoidea, and plumula, equally con- 
ceal their shells. , 
«The circumstance of some of the naked 
limaces possessing a shell internally, the ana- 
to ical enquiries of Swammerdam and Lis= 
indeed of the one figured in this work was not simple, but composed ef 
