C O N C H O L O G Y. 19 
elafles them under mol! q fea, diftinft from (hells; while, 
on the other hand, Buonanni and Grew, who rank them 
with the teftacea, place them as univalves; and Wood¬ 
ward, Argenville, Gualtieri, Breynnius, Davila,and Meuf- 
chen, rank them as multivalves. This latter difpofition 
is certainly very erroneous; for, though they define the 
many futures feen in echini as fio many valves, yet they 
cannot in anywife be reckoned as fuch, for they have no 
play or motion whatever, as valves, but are mere joinings 
of ieveral pieces, always permanent and fixed. Neither, 
indeed, would the name of multivalves anfwer to all echi¬ 
ni, could the futures be termed valves'; as only fome ge¬ 
nera, not all echini, are compofed of fuch futures. 
It was a long time before any regular orfyftematic ar¬ 
rangement of (hells took place. The moll general manner 
of the old authors has been to divide all (hells into fimple, 
turbinated, and bivalve: but it is evident that this divi¬ 
sion was very erroneous, becaufe it excluded the multi- 
valves. Succeeding naturalifts, inftead of this arrange¬ 
ment, fubftituted three other divilions, viz. univalves, in 
which they comprehend both the non-turbinated and tur¬ 
binated ; bivalves, or double (hells ; and multivalves, con¬ 
fiding of many parts. This being now the generally-re¬ 
ceived divifion, on which cuftom and philofophy have 
ftampt an authority, we (hall adhere to it in this treatife. 
Each of the above three general diviftons contains many 
families, genera* and fpecies. Mr. Tournefort obferves, 
that there ought to be certain principles or charafters in 
everyfyftem or method; which principlesorcharaftersfbould 
always be taken from the chief part of the objeifs, and not 
from feveral parts. This charafter (hould alfo be the con- 
ftant one through the whole fyftem, to preferve a perfect 
regularity. Thus all bodies which agree in one fixed 
charadter form the clafs, and the affinities or differences 
of thofe bodies to each other in the lefs principal parts, 
create the fubordinate genera and fpecies'. On this maxim 
Da Cofta has founded his fyftem ; for all the turbinated 
univalves, he has fixed on the aperture or mouth of the 
fliell as its effential charadter. For the bivalves, on the 
hinges ; and for the multivalves, on the number of valves. 
The fimple figure, the chambered Itrudture, and the latent 
whirls of the revolved (hells, which are the only remain¬ 
ing univalves not charadterized by the mouth, fuch as 
the limpets, ammonia, and cowries; thofe are the effen¬ 
tial charadters for fuch families. In the fubordinate di- 
vifions of genera or fpecies, the following charadters are 
fufncient: i. The figure or (hape. 2. The turban or cla¬ 
vicle. 3. The work on the fliell. 4. The other lefs effen¬ 
tial particularities; as, thicknefs or thinnefs of the fliell, 
the epidermis, and the fubftance, whether pearly, horny, 
or opake. 
Of UNIVALVES, or SINGLE SHELLS. 
Writers on conchology have laid down one natural me¬ 
thod for the arrangement of univalve (hells, which ought 
to be adhered to as fcrupuloufly as poffible; that is, to 
begin with the limpleft forms, and proceed upwards to 
thofe which are the mod complex. According to this 
method, the vermiculi, or worrp-fliells, which-include the 
ferpula, toredo, and labella, undoubtedly (land firft ; then 
the dentalia, or tu(k-like (hells; next follows the patella, 
or limpet; and then the aures-marinte, haliotis, or fea- 
ears. Thele conftitute four families, and form the firft 
general divifion, called fimple univalves.- 
The (hells of the next limpleft configuration are claffed, 
by Da Cofta, under one family, and divided into fix ge¬ 
nera, viz. the orthoceratites; the lituitse, or croziers; the 
turbines polythalmi; ammonia; ammonoidas; and the 
nautilus, or nautile. Thefe being all of them chambered 
(hells, form the 1 next general divifion, which is called con- 
camerated univalves. 
Next follows the fixth family of (hells, which is divided 
into three genera,'viz. bulls, called pewit’s eggs, or dip¬ 
pers; femiporcellanas, which are alfo the bulla kind, but 
greatly refembiing the porcelains; cypres, the porcelain 
(hells, or cowries. This family conftitutes the third gene¬ 
ral divifion, called revolved univalves. 
The next arrangement of (hells Da Cofta forms into ten 
cliftin6b families, making in the whole fixteen families of 
univalves. In this arrangement he place’s firft, the argo¬ 
naut, or paper nautilus; fecond, the aures-coehleae, or 
eared lnails; third, the olives, a fpecies of volutes, call¬ 
ed cylindars; fourth, the volufse, or cones, called ad¬ 
mirals, &c. fifth, globofse, or globofe, (hells, fuch as the 
tuns, melons, Perlian crowns, &c. fixth, cafTides, or hel¬ 
mets, which are a fpecies of buccinum ; (eventh,' trocbi, or 
tops, (hells of a top-like or pyramidal fhape; eighth, coch¬ 
leae, or ear-formed (hails ; ninth, buccina, or whelks ; and, 
tenth, murices, or rock-lice (hells. Thefe families are 
fubdivided into many genera, and conftitute the fourth 
and laft general divifion of the firft order of (hells, called 
turbinated or fpiral uniyalves. We now proceed to explain 
thefe divilions in their natural order. 
OF SIMPLE UNIVALVES. 
The mod fimple (hells are certainly thofe that envelope 
the vermiculi or fea-worms, which, in their generic cha- 
rafter, are called terebella , the piercer or borer; and they 
are, in many refpefts, very deltruftive creatures. The 
elTential charafter of this family is thus defined by Da 
Cofta: tubular cylindric (hells, fingfe, often in mafles to¬ 
gether, or adhering to other extraneous bodies ; varioufly 
(inuous, by winding or twilling to and fro, in various 
contortions; whence they are of no determinate or regu¬ 
lar (hape; or they are rather of divers fliapes and forms. 
Dr. Gmelin divides them into the three following genera : 
SERPULA, TOREDO, and SABELLA. 
The firft genera of thefe cruftaceous worms produce- 
their (hells in very great variety ; and in their windings 
and convolutions are fonietimes Co regularly fpiral, as ai- 
rnoft to emulate the mod perfeft turbinated (hells ; but 
this is, perhaps, quite accidental. The molt general form 
in which thefe (hells are found, is (imply tubular, ^nd in 
clufters, varioufly coloured, and of different fizes, which 
indicate their progreffive (late of growth. They are found 
from the (ize of a (talk of grafs, to that of a fwan-quili ; 
and fometimes as large as a man’s finger. Some are of a 
dull white, others grey, yelloivifli, and brown. As they 
are often found in large lumps, attached to other bodies 
in a fpiral form, and other (hells as frequently attached 
to them, they were long miftaken by the earlier naturalifts 
for a fpecies of coral. They inhabit various parts of the 
European fea ; and thofe defcribed by Davila are natives 
of the Mediterranean and the Venetian gulf. They are 
alfo found on the coafts of Coromandel and Malabar, in 
the Indian ocean, and in the African, Afiatic, and Ame¬ 
rican feas. There are thirty-eight fpecies of them. 
The Teredo is that pernicious animal fo deltruftive 
to the bottoms of (hips. The fliell is tapering, flexile., and 
capable of penetrating wood. There are only three (pe- 
cies known, the na-valis, uiriculus, and clava. The na- 
valis is the (hip-worm ; whence it takes its fpecific na,me. 
It is an inhabitant of the Indian feas and from thence 
it was firft imported into Europe. It penetrates eafily 
into the ftcutelt oak-planks, and produces dreadful de- 
ftruftion to the (hips by the holes it makes in their (ides; 
and it is to avoid the effefts of this creature that veffels 
require (heathing. The head is well prepared by nature 
for the hard offices which it has to undergo, being Goated 
with a ftrong armour, and furniftied witli a mouth like 
that of the leech ; by which it pierces wood, as that ani¬ 
mal does the (kin ; a little above this it has two horns 
which feem a kind of continuation of the fliell; the neck 
is as ftrongly provided for the fervice of the creature as 
the head, being furniflied with feveral ftrong mufcles 5 the 
reft of the body is only covered by a very thin and tranf- 
parent (kin, through which the motion of the inteftines is 
plainly feen by the .naked eye; and by means of the mi- 
