354 HELMIN' 
elaffes or families, according to the form or character 
of.their (hells, viz. i. Umbilical, efedt, with the pillar 
perforated ; examples of which are, trochus perfpcBivus , 
exhibited in the Conchology Plate IX. the ille 11 
placed in the centre : trochus manus, left hand corner of 
the fame plate at topi-: and trochus .cinerarius, fig'. 14 and 
15, in the Helminthology Plate IV. 2. Imperfo¬ 
rate, ere£l, with the umbilicus or navel clofed ; a fpe- 
cimen of which is given in the Conchology Plate, IX. 
the right hand corner at top : it is the trochus tuber. 
3. Tapering} with an exferted pillar, and falling.on one 
fide when fet upon the bale ; exemplified in trochus 
telefcopiunx , twelve beautiful varieties of whidh are exhi¬ 
bited in the Conchology Plate IX. placed, all round,' 
with the points towards the centre : theft are named 
by fome conchologifts , pyra.midella, or pyramidal (hells. 
The animal, in all three of the divifions, is a limax. 
Turbo, isa very extenfive genus ; and fome of the 
fhells belonging to the animals of this clafs are of 
prodigious value. Many of them appear to be clofely 
allied to the bucciniim genus; but are readily diftin- 
guiffied by attending to the Linnaean generic clraradlers, 
viz. “ fpiral folid ; aperture orbicular, and contracted.” 
Theft turbinated fiiells have been ufually called wreaths. 
The animal is a limax;. and the number of fpeci,es 
amounts to one hundred tmd fifty-one, which are 
arranged in five diftindt families, according to^the fimi- 
litude of their fiiells. r. Thofe with the pilla’r-inargin 
of the aperture dilated, and imperforate; as exem¬ 
plified in tuhbo littoreus, the common perriwinkle. 2. 
Solid, and imperforate, as in turbo chryfojlomus , exhi¬ 
bited in the Conchology Plate X. fig. 13, 14; in that 
beautiful fpecimen turbo farmaticus, delineated in the 
fame engraving at fig. 12 ; and in turbo cidaris, fiiown at 
fig. 15, 16, in the fame-plate. 3. Solid, and umbilicated 
or perforated ; as in turbo delphinus ; twelve elegant 
varieties of which are given in the Conchology Plate 
XI. 4. Cancellated ; as in that rare fpecies turbo fca- 
laris, the wentle-trap; delineated from nature in the 
Conchology Plate X. fig. 17 ; ,it is a fhel 1 in great 
eftimation. 5. Tapering ; as exemplified in turbo tercbra, 
Conchology Plate XIV. fig. 9 ; and in turbo imbricatus ; 
exhibited in the two circular arrangements of tapering 
fhells, in the Conchology Plate XII. The wentle-trap 
in this genus, and the cedo nulli among the cones, are 
the . molt valuable of all fiiells in colledtions. See 
Concho 1.ogy, vol. v. p. 26,27. 
Helix, a molt numerous genus, containing the whole 
tribe of fnails, which amount to no lefs than two 
hundred and fixty-feven fpecies, deftribed in p. 327- 
330, of this volume. Several of them are figured in the 
Conchology Plates as there referred to; and the helix 
vivipara is delineated In the Helminthology Plate IV. 
fig. 10. The fnails, nerits, and fome fimilar families, 
were formerly known under the common name of cochlea. 
Nerita, a genus in which the fpecies are in fliape 
and form not far removed from the helices ; yet fo as 
to be very diftinguifilable on a flight view. The animal 
is a limax ; and there are feventy fix fpecies, which are 
fnbdivided into three tribes or elaffes, according to the 
faffiion of their fiiells. 1. Umbilicate ; aperture femi- 
orbicular or femi-lunar ; as may be feen exemplified in 
nerita canrena , Conchology Plate X. fig. 3,4; the twenty- 
feventh variety. 2. Imperforate, lips fmooth or tooth- 
lefs ; as in nerita radula , delineated in the Conchology 
Plate Vv the two corner fhells at top. 3. Imperforate, 
with the lips dentated; as in nerita exuvia, reprefented 
in Conchology Platg X. fig. 1, 2. 
Haliotis is a genus of which the animal is a limax, 
included in an ear-lhaped fhell; whence the name. 
There are only nineteen fpecies at prefent known, which 
gre defcribed under the article Haliotis, p. 177, of 
this volume; and a corredt delineation of one of the 
fiiells, haliotis iris , is, given in the Conchology Plate 1. 
fig. 9. Some conchologifts admit it as a collateral cha- 
r H O L O G Y. 
racier of the haliotis, that the infide is always of the 
fined pearl, and pearls are oftentimes produced in thefe 
fiiells. See Conchology Plate V. fig. 2. The perfora¬ 
tions vary in number in different fpecies. It has been 
obferved, that the animal always clofes one of thofe 
holes towards the fpire, whenever he opens another to¬ 
wards tile head, as he grows bigger r, and by that means 
the number of openings is invariably the fame in dif¬ 
ferent individuals of the fame fpecies., Shells of this 
genus are very rarely difcoVered fofiil ; and it is to be 
doubted whether any of thofe defcribed by writers are 
truly of this genus. 
Patella, .is the mod extenfive genus of all the tef- 
taceous tribes, comprehending no lefs than two hundred 
and forty fpecies-:, the animal, is a limax; and the 
(hell is.fub-conic, and without fpire. 
They are named limpets , from their refemblance to a 
little plate, (patella ;J and are more or lefs conic with¬ 
out, and concave within. Some fpecies have the apex 
or top entire; others perforated; the 1 chambered lim¬ 
pets are diftinguiffied by a peculiar kind of projedling 
procefs, or lip Within; mod have the margins entire, 
but fome have an indent or fiffure in that part; and 
others are fo completely fpiral or wreathed in their ex¬ 
terior appearance, that they referable rather the trochi, 
or top-ihclls, than the limpet. They are arranged in 
five diftindt fedtions or families, viz. 1. Labiatae, fur- 
niflied with an internal lip ; (hell entire. 2. Dentatse, 
with the margin angulated, and toothed. 3. Mucro- 
natas, with the pointed tip recurved; 4. Integerrimae, 
very entire, and not pointed at the tip. 5. Perforata;, 
with the crown perforated. Thefe fhells genetically 
fuborbicular, fhield-form, or bonnet-fliaped, as exem¬ 
plified in Conchology Plate I. fig. 4, 6, and 8, called a 
nialk limpet; fig. 5, i?the ftellated limpet.; fig. 7, a 
’ chambered limpet, patella aculeata. Thefe are fome of 
the mod beautiful (hells afforded by the numerous race 
of limpets. See alfo the Helminthology Plate IV. fig. 17. 
Dentalium, a genus of which the animal is a tere- 
bella, inclofed in a tubular (hell, open at both ends, 
(lightly curved in fome fpecimens; ftraight in others ; 
but they are all called tooth-fhells. There are twenty- 
two fpecies now afcertained, of which the two hand- 
fomeft are, dentalium elephantinum, delineated in the Con¬ 
chology Plate I. fig. 2 ; and dentalium entails, exhibited 
at fig. 3, in the fame Engraving. , 
Serpu l a, a genus of tubular worms, feveral fpecies of 
which are found adhering to other fubftances, in cluftersj 
whilft othersare quite feparate and detached. The animal 
is a terebella ; and there are forty-eight fpecies. Of the 
adhering kind, a fine fpecimen is given of ferpula contor- 
tuplicata, in Conchology Plate I. fig. 1 ; and in the Hel¬ 
minthology Plate IV; is exhibited the Jerpula fpirorbis t 
fig. 18,, magnified, and 19, its natural fize. 
Teredo is the deftruclive genus of (hip-worms. 
The animal is a terebella, furniflied with two calcare¬ 
ous hemifpherical valves, truncated before, and two 
others of a lanceolate form, penetrating wood. This is 
a terebella of a peculiar kind ; the body being of a foft 
and gelatinous nature, but having "the head provided 
with an inftrument of a calcareous fubftance, Which 
performs the office of an augre, and penetrates the hard- 
eft oak. The mod deftrudtive of the geiius is the teredo 
navalis , which perforates the bottoms of (hips, and ren¬ 
ders the invention of coppering the bottoms highly ex¬ 
pedient. Thefe worms were originally imported from 
India into Europe, about feventy years ago. Three 
fpecies only of this fingular genus have been yet difco- 
vered, and which are named navalis, utriculus, and 
clava. 
Sabella, is the laft genus of teftaceous worms, and 
appears to be the connedting link between this order and 
the Zoophytes; among which Ellis placed it. The ani¬ 
mal is a nereis, with ringent mouth, and two thickifli 
