196 He Hijiory of ANIMALS. 
Animals living under the defence of Jhelly coverings . 
Series the Fourth . 
CENTRONIX ^£ 5 ge-Uog§, 
T H E Centronix are animals living under the defence of a fhelly covering, form¬ 
ed of one piece, and furniffied with a vaft number of fpines, moveable at the 
animals pleafure. 
The animals of this feries have been called by authors Echini Marini, Sea Hedge¬ 
hogs, from fome refemblance, in the prickly furface of the fhell, to the coat of the land 
animal of that name 3 but this is a very poor charaderiftic from which to name a clafs 
of animals, whofe whole ftrudure is full of eflential marks of diftindion. 
It has been warmly difputed, between authors of note in thefe ftudies, whether the 
Centronix, or Echini Marini, as they call them, belonged properly to the teftaceous 
or the cruftaceous animals, that is, whether they were to be arranged among the ordi¬ 
nary ffiell-fifh, or among the crab and lobfter kind 5 it is eafy to determine the contro- 
verfy, by obferving that they belong to neither: their charaderiftics, the ftrudure of 
their bodies, and even the form, ufe, and intent of their feveral exterior parts, ufually 
comprehended under the term, fhell, are wholly different from thofe of all other 
creatures3 and though all the fpecies are referable to the fame clafs, and, indeed, in 
ftridnefs to the fame genus,, yet they are a diflind feries of animals by themfelves, and 
demand to be placed accordingly. 
Centronia fuhglohofa papillis minor thus, tOUtlU 
*The roundijh Centronix with fmall papillce . 
This is a confiderably large fpecies5 we ufually meet with it of about an inch and a 
half in height, and as much in diameter, but it often grows to three times that fize » 
it’s figure is nearly round, but fomewhat depreffed at the bottom 3 it’s covering, which, 
as in the fhell-fifh, is the thing principally demanding our attention, is formed of one 
fingle piece, and is of a fhelly ftrudure and hardnefs: in the center of the bafe there 
is a large, roundifh aperture, at which is placed the mouth of the animal 3 and on 
the fummit there is another aperture, fmaller than the former, but of a like roundifh 
figure, out of which the creature voids it’s excrements: the colour of the whole fhell 
is a dufky reddifh, with an admixture of whitifh, and often of greenifh : it is covered 
with ail innumerable multitude of papilla?, which are fmall, and difpofed in regular 
lines from the upper aperture to the lower : ten of thefe lines, difpofed into five pairs, 
are formed of papillae larger than the reft, and make a pretty figure on the fhell 3 they 
are all elevated, more or lefs, above the reft of the furface of the fhell, and give origin 
to a multitude of fpines, which arm the whole furface, and give the creature, while 
living, and under water, that appearance of the hedge-hog, from which it has been 
named Echinus: the fpines are about a third of an inch long, and very flender 3 they 
are of a reddifh colour, and are pointed at the extremities 5 they are all moveable, by 
means of tnufcles affixed to their bafes, but they are apt to fall off, when the creature 
is dead, on the flighted: touch : befide thefe fpines, which are more than two thou- 
fand in number on this fpecies, there are about twelve hundred apertures in the fhell, 
out of which the creature thrufts fo many flefhy tentacula or filaments at pleafure, 
by means of which it fixes itfelf to the bottom : the fpines ferve it, on the contrary, 
by way of legs, to move forward with, and for it’s defence, and feveral other purpofes j 
the natural pofture of the creature is, with the broad or depreffed part, called the bafe, 
toward the bottom : at the aperture, in the center of this, is fituated the mouth, which 
is furniffied with five fharp teeth, fixed at the extremities of five little bones, in the cen¬ 
ter of which is placed the tongue 3 the bafe of this is a caruncle of a rounded form, 
and the whole is flefhy: from the hinder part of the mouth there begins an inteftinal 
canal, which is carried in feveral volutions round about the infide of the fhell, to which 
it is fixed by a multitude of fine fibres 3 it finally terminates at the aperture, in the 
top of the (hell. 
Thus 
