15 
CONCH 
ronlertt, by the obvious charafters of teeth, plumage, and 
tins; characters that cannot beheld in any other light, 
than as analogous to the external characters, or the (hells 
of teftaceous animals ? Such an abftrufe method, were it 
even attainable, is the lets neceifary, becaule every ac¬ 
curate and judicious naturalift may always be capable of 
diftinguilhing the fpecies by the (hells alone, though he 
has many of the.fame kind, and of very different appear¬ 
ances, before him ; for every fpecies of (hell has one or 
more particular (pacific character, either in work, colour, 
or fubitance, which it retains through all its various ftages 
and forms, and is therefore always to be diltinguifhed and 
known by it. 
Mr. Adanfon drew a condufion of the different (hells 
he propofes for the fpecies of the black limpet, from the 
(ituation of its eye or beak being at two thirds of the 
length of the (hell. This fitnation of the eye, he, for 
want of accuracy, thought to be a particular charaCfer of 
the black limpet; but he overlooked that the eyes or 
beaks of many other fpecies of limpets are placed in like 
manner, or at two-thirds the length of the (hell. He 
therefore erred as much in making that particular the 
„ criterion of the (hell, as in making the fifh only, the cri¬ 
terion of the whole animal, or fi(h and (hell. But there 
are, on the contrary, many infallible characters upon 
/hells, by which the family or genera may be diltinguifhed 
from all others. The goat's-eye limpet wears, perhaps, 
. as many different appearances as any lpecies of (hell, and 
even often greatly refembles others; but look only on its 
ridges, the character of which is to be three-edged, like a 
triple-edged lpear or l'word, and it is immediately recog¬ 
nized through all its different appearances. The garnet 
limpet has, m like manner, many different appearances ; 
neverthelefs its elegant garnet-like femi-tranlparent eye 
or top always characterizes it through all its colours and 
forms. The finall blue-rayed limpet of our own coaft is, 
when youpg, thin, horny, and very conical; when old, 
thick, flattilh, and misfhapen; yet its few blue ffreaks 
always characterize it. The bloody-tooth nerit is known 
through all appearances, by the blood-like (pots on its 
teeth. Each volute has fome particular ftreak, band, 
fpot, or colour, which it uniformly preferves through all 
its ltages. Even the rocks or murices, the fpiders, and 
the winged (hells, whofe appearances in their feveral 
growths, above all other (hells, are fo extfemely different, 
that when young they have narrow, (harp, even, thin, 
and fmooth, lips, and the opening is pretty clear or free; 
when old, this lip is greatly extended, very thick, pronged, 
or let with large fpikes, and almoll doles their mouth or 
opening. Yet even all thefe (hells, either in the turban, 
body, tip, work, or colour, have conifant and fixed cha¬ 
racters, which diftinguilh them throughout all thele ex¬ 
tremely different appearances. But it has been objected, 
that the (hells alter in every ftage of the animal’s growth; 
and that hence enfues a very confiderable change in the 
forms and colours of the lhells. If fo, it evidently fol¬ 
lows, that the animals themfelves mult undergo as ma¬ 
terial changes in their forms. It cannot be otherwife; 
for the (hell mult always anlvver to the animal, and its 
inode of life j therefore, if great changes happen to the 
animal as well as to the (hell, we remain in equal un¬ 
certainty as to an arrangement by the fifli, as by the (hells; 
but as the (hells have the molt obvious and eligible cha¬ 
racters, and are more eafily attainable, the methodical ar¬ 
rangement of the fubjeCts in conchology (hould be made 
from the (hell. The inveftigation of the included living 
animals, forms a branch ot Ichthyology, and will accord- 
f ingly be found under their generic names in this work, 
taken from the Linnrean clalhfication. 
On the FORMATION, GROWTH, and COLOURS, 
of SHELLS. 
P. Wolfgang Knorr, in his Delices de la Nature, has 
given the iollowing account of this department of animal 
phyftolcgy. Every (hell animal, like the other vermes, 
O L O G Y. 
is at firft very minute, and fprings from little eggs or ■ 
fpawn formed in a kind of froth, which is expelled by 
the parent animal. This froth confifts of a great many 
cells or cavities, refembling the honeycomb of bees, and 
is called melicera. The largenefs of the fpawn is pro¬ 
portioned to the natural ftze of the (hell; and it is taken 
for granted that the fpawn of a large buccinum, ought to 
be larger than that of a little nerite, for the fame reafon 
that the egg of an oftrich differs in fize from that ot a 
goldfinch. But the fubjeCf has not yet been fufficiently 
examined to make this part of conchology clear and ob¬ 
vious. What we have noticed on this head, is neverthe¬ 
lefs worthy of confideration and regard. 
The fmalleft (nails are formed with their (hell,’but which 
at firft is fo fine and brittle, as not to bear the (lighted 
touch of the finger. The animal alfo is delicately fa- 
(hioned. The manner of the procefs is certainly enve¬ 
loped in darknefs, and we yet want many experimental 
obfervations on the formation apd growth of fiielis. Every 
(hell-animal (cents to be the architect of its own habita¬ 
tion ; and, although this may appear doubtful with re¬ 
gard to the paper nautilus, yet there is a mode in which 
we may (hew, as far as observation goes, the conforma¬ 
tion and growth of that (hell. The animal is obvioufiy 
compoled of different fibrous, mufcular, and membranous, 
parts ; it has many feparate organical refervoirs, humours, 
and pores, and alfo a clammy fubitance, which covers the 
whole flelh, and makes it flippery and tenacious. This is 
nothing but the moifture that flows continually from the 
whole body, perhaps from millions of pores, and is found 
all over the furface of the animal; and being of a calca ¬ 
reous nature, it in time gets hard ; and, in proportion as 
it is forced out lucceffively by the humid liquor, it at 
length detaches itfelf entirely from the body, and thus 
becomes as it were a diftimft covering. It is probable that 
the (hell is not folid throughout, but that it contains a 
number of minute fpaces, anfwering to the pores of the 
animal, from whence flow the matter which torms the 
(hell; conveying a portion of juice fucceffively to the in¬ 
ner furface of the (hell, penetrating through thefe fpaces 
to the upper or external furface, and thus making it both 
harder and firmer. 
The conftruCtion of the (hell mud necefiurily follow the 
natural conformation, and hence it will be lmooth, tu- 
berculated, llriated, curled, rough, or wrinkled, accord¬ 
ing as the animal is to be in time evolved. As (bon as 
the creature has taken fo much growth that it can no 
longer lodge in the (hell, the increafe is faid to be made 
after the Iollowing manner: It thru Its from the orifice 
that part of the body which it can no longer cohtain in 
the (hell. That furface being naked, continues to dif- 
charge the fame moilture, which hardens, and, uniting 
with the edge of the orifice, forms a new portion of (hell, 
which prefently becomes exactly fitted to that piece of the 
body, which, from the place being too narrow, it obliged 
him to expole. When the animal is attached to the inner 
part of the (hell, the moifture diffolves in the former tu¬ 
bercles, and makes that firm. From thence arife the fpires 
in fnail (hells, and the rings in the helices; the mark of 
addition to which we may always fee, although the bed 
for the new moifture, which is depoftted on the edge, be¬ 
ing hardened afterwards, is very narrow and fine. In 
fome of thefe animals, when they arrive at a certain age, 
the ftrufture at the extremity is changed by the addition 
of new lobes, as it happens in many other, parts which 
do not grow but in a certain age ; as the horns, the teeth, 
&c. fo the mouth of the (hell neceffarily takes a different: 
form thereby. This may be obferved in fome lpecies of 
the buccinum, which have at firft the mouth united, but 
afterwards forms a projecting lobe, and are.wry-mouthed, 
wrinkled, or broad, (o as to be taken by fome naturalifts 
for a different genus ; on the fame ground of error, which 
led fome of the early naturalifts to rank a ftag with horns 
under a diftinft fpecies, in order to diftinguilh it from a 
fawn, whofe horns had not begun to (hoot forth. 
According 
* 
