351 
HELMINTHOLOGY. 
Scylljea, is alfo very fmall, with a compreffed 
body, and three retractile tentacula on each fide: they 
are generally attached' to fea-weed.' 
Luckrnaria, is an animal confiding of a lump of 
jelly, without head or eyes; it however protrudes an 
arm from the angles of the body, each of which is 
furnifived with from thirty to forty tentacula, retractile, 
and employed .in patching its prey, which it turns into 
an orifice in the centre of its mats of body. 
Physsop'hora, is a very curious little creature, 
hanging pendant from an aerial veficle, with fellile mem¬ 
branes at the Tides, and radiated tentacula beneath, 
whereby it has the appearance of a full-blown flower 
hanging' downwards. 
ClaVa, is a fmall fixed animal, with no other motion 
than what is afforded by its dilatable mil fetes, which 
enable it to erect its body ; having a vertical month at 
the top, fed by a border of tentacula, which gives it 
the appearance of a flower. 
Salpa, is a worm of an elongated form, inclofed in 
a tube, open at each extremity. They are of a grega¬ 
rious nature, and fwim in company with great facility ;’ 
poffefiing the power of contracting or opening at plea¬ 
sure the cavity of their extremities : they'are yery tranf- 
parent, and exhibit a rich appearance of varying colours. 
Da g Ys a y- is a worm about three inches long, inclofed 
in a tube open at both ends, and very like’the Salpa. 
The genus Asterias, known by the common name 
of Jlar-JiJk, contains a great number of very beautiful 
fpecies, inhabiting all feas, and forming an amazing 
number of varieties, yet all rayed in fuch a manner as 
to have fome refemblance to a ftar, wherefore they are 
alfo called fea-Jiars, and are by that character inflantly 
known to belong to this genus. We have deferibed them 
at large under the article Asterias, vol. ii. p. 300-302; 
where the mod curious fpecies of them are engraved on 
the corfefpondent plates. 
But of all the genera comprifed in the order of Mol- 
lufc'a, the greatefl variety of beautiful tints and curious 
forms is produced by the Echini, many of which are 
highly valued in collection's. We have deferibed no 
lefs than one hundred and nine fpecies, (all at prefent 
known,) and given plates of the mod rare and ftriking 
individuals, in our lixth volume, p.227-234, to which 
v/e beg to'refer tiie reader.—'All the other genera are in 
like manner deferibed under their proper titles or names 
in this work, where engravings are. given of the mod 
'intereding fpecies belonging to each genus. 
TESTACEOUS, or SHELL WORMS. 
This extenfive order of Vermes, gave birth to tiie 
elegant fcience of Conchology, or methodical arrange¬ 
ment of fliells; and from one of its genera, the Argo- 
nauta, or nautilus, it is even faid that navigation, or 
the art of deering a Ihip at fea, fird took its rife ; whence 
the allufion in Pope : 
“ Learn of the little Nautilus to fail.” 
The animals which form this order are of a Ample 
druClure, gelatinous, and foft, being no other than Mol- 
lufcae, with the addition of a calcareous habitation; 
the rudiments of which being.formed, in their embryo 
. date, they carry it with them during'the whole of their 
lives. Some of them are diflinguifhed by fliells formed 
of feveral fegments or valves, whence they are denomi¬ 
nated multivalves. Others, whofe habitation confifis of 
two fliells, as the m'uffel, oyder, and cockle, kinds, are 
termed bivalves ; and thofe which have only one fliell, ' 
are called univalves. Thefe three clafles are fdbdivided 
into genera, which are formed upon charafteriflical dif- 
tindtions, arifing in the fird clafs from the form and 
number of the valves; in the fecond from the number 
and kind of articulations in the hinge; and in the third 
from their fpiral. turn, form of the aperture or mouth, 
teeth, pillar,Jkc. See the article Concholog y, vol. v. 
p, 14-41. 
In the-artificial arrangement of fliells, it lias been the 
cufloni of mod conchologids to begin with the uni¬ 
valves, and to end with the multivalyes; but Linnaeus, 
in erecting, this order of the animals which inhabit the 
(hells, has quite reverfed the method, beginning with the 
lnulrivalves and ending with the univalves. For this ar¬ 
bitrary devi 1 tion, as well as for mixing and incorporating 
fo many fliells of adverfe fliapes and different forms in the 
fame genus, Linnteus has been called a bad concbolo-. 
gid, and fubjefted to much eenfure; but certainly with¬ 
out reafon, 1 fince his generical characters hold flriftly 
throughout the whole, and hence afford an unerring 
criterion of affinity and, family connexion, the great ob¬ 
ject of his claffificatien. A id with refpedd to his being 
,a bad conchoi.ogid, his own declaration on this point- 
Hiould be known, viz. “ that he would leave the whole 
order of Tejlacea untouched, if he could not get .at the 
animals, rather than content himfelf with deferibing. 
their mere houfes.” Hence it is obvious that his en¬ 
quiries, as a great naturalid, were directed to the ha¬ 
bits arid,,economy of the 'living, annual, and hot, as a 
conchologid, to dead matter, or the exterior of a fliell. 
See Linnaean TranfaCtiohs,' -vol. ii. p. 15. 
His fird genus, in the order of tedacea, is the Chiton; 
fliell confiding of many valvCs, and its inhabitant a do- 
ris. Tliey are found in almoft every fea ; and confifl of 
twenty-eight fpecies; one. of which, chiton magellamcus, 
is delineated in the Conchology Plate XVI. fig. 4. vol. v. 
Lepas, is a,genus oi" multi valves, confiding of thirty- 
two fpecies, divided into two clafles, viz. balani, or 
acorn (hells, and anatiferg, or barnacles. The animal is 
a triton, covered with many unequal ereft valves, which 
produce a Angular appearance. The mod curious of 
them is the lepas anatifera, or barnacle goofe, exhibited 
in the above-mentioned Conchology Plate, fig. 6, 7, and 
iff, which is the mod rare variety. The balani, or 
acorns, are. of different fpecies; as the Indian crown, 
( lepas tnitclla,) fhown at fig. 5 ; and a bunch of acorns at 
fig. 8. They -are found plentifully on the Britidi ffiores, 
and on the fea-coads of every qountry. 
Pholas, is the third and lad genus, of the multi¬ 
valves ; in wliKh there are twelve fpecies. Linnaeus! 
calls it a bivalve', with acceflory valves at the hinges. 
The animal is an afeidia, which has the Angular pro¬ 
perty of infinuating itfelf, while young, into foft porous 
done and wood, and as it increafes in fize it enlarges its 
habitation within, and'thus at length becomes impri- 
foned. Thefe animals were formerly called piddocks ; 
and are furnilhed with a phofphoric liquor of great Bril¬ 
liancy, which illuminates whatever it touches or hap¬ 
pens to fall upon. A back and front view of the pholas 
daElylus is given in the above-mentioned engraving, at 
fig. ii, and 12.—For the curious habitudes and natural 
hiflory of this Angular-genus/ fee the article Pholas... 
With BIVALVE SHELLS. 
Of thefe there are fourteen genera, exhibiting a great 
variety of different forms, and fplendid colours. The 
Mya, or pearl-oyder, is an afeidia; and the lpecies of 
this genus were ranked with the muffels, till Linnaeus 
parted them. They refide chiefly at the bottoni of the 
waters they inhabit, burying thenifelves,'like the mnfi. 
fels, in the fand, clay, or mud ; and hence the fifhing 
for them is attende-d with conliderable difficulty. There 
are tweiity-fix fpecies; the molt valued of which is the 
mya margaritifera, or true pearl-oyder. 
Solen, is a ge'nus in which the inhabitant is alfo an 
afeidia, commonly called the razor-Jheath, or knife-han¬ 
dle, from the elongated form ot its fliell, many of which 
are very beautiful. There are twenty-three fpecies; one 
of which, the folen radiatus, is correftly delineated in 
the Conchology Plate XV. fig. 5. The Linmean folens 
are divided by foreign.writers into three different genera, 
two of which comprehend'the recent kinds, the third is 
edabliflied chiefly for the reception of fome foffil fliells, 
fuppofed 
