( ) 
pura^ and the reft of the teftaceous frthe ; and yet he 
ownsth^it RoHJeletius reckoned them among the Cru/fa- 
ceous Kind, and accordingly difcourftd ot them after 
Crahs and Lohjlers^ juft before he treated of thofe Ani- 
mals, which are confefledly teftaceous ; wherein he foJ- 
lowed Pliny ^ who was of the fame Opinion before him. 
And ihey certainly were in the right, tho* for want 
of ftating the true difference between a Cruft and a 
Shell properly fo called, the due place which the Echini 
ought to hoJd in a Natural Hiftory of Shellfifh, as the 
word may comprehend both Kinds, has never yet, that 
I know of, been aftertained. 
A Shell properly is fuch a hard Subftance, as covers 
an entire Animal, or at leaft one whole fide, without 
Joynts or Ligatures, as in Bucctna, Purpura^ Murices^ 
Oyflers, Scallops^ Cockles, and the like. A Cruft is fuch 
a hard Subflance as covers only one particular Joynt of 
the inclofed Animal, fb that in the whole Crufta- 
ceous Trile there are as many Shells upon every 
Animal , ( if I may be allowed to ufe that word 
in a larger fenfe ) as there are Joynts in that Ani- 
mal. This is plain in Crals^ Loh^ers^ (^^^1'fifl>^ and 
Shrimps ; for which Reafon Cruftaceous Animals may 
truly be called Multuteftaceom, and the other fimply 
teftaceous^ or hi teftaceous. And therefore as in Scaly 
Fijhes, every Scale has a correfpondent Mufcle^ to 
which, by a particular Tendon it is annexed fo all 
Cruflaceous Animals have particular MufcleSt which are 
inferred into every Cruft ; all which Cruft s are alfo con- 
nefted each to the other by common Membranes, which 
here are in a more efpecial manner neceflary, be- 
caufe they do not lie imlricatim upon one another as 
Scales do. 
As plain as this (eems to be, Ariftotles definitions of 
Cruftaceous and Teftaceous Animals^ or, (as he calls 
them) ViaLXa.nja<^^f{cf. and ^Os^s^Ko^^fjio, have been uni- 
verflally 
