(94 ’ 
CLASS VI. CRUSTACEA. 
Remarks. These animals were placed in the 
class Insecta by Lineas. There was no difficul- 
ty in this arrangement, as the characters are deii- 
nite and constant. The separation is generally 
approbated. In truth there seems to be a wide 
difference between a lobster and a butterfly. But 
some species of the class Insecta have something 
of a crust, which causes many naturalists to ques- 
tion the beneficial uses of this subdivision. 
They respire by a kind of gills or lamellar py- 
ramids, sometimes furnished with threads. These 
are placed at the articulations of the body. They 
generally have four antenne. Their crustaceous 
covering is very strong in some species, as the lob- 
ster ; in others it is thin and tender. 
The crusts of some species have been found in 
the state of petrifactions or relique. But I do not 
think Brongniard has demonstrated the trilobite 
to have been of this class. I have recently found 
trilobites in a calciferous slate, with their carbo-: 
nate of lime shells still remaining. I believe M. 
Brongniard will hereafter convince himself that 
the trilobite was a multivalve molluscous animal. 
ORDER 1. DECAPODIA. 
Head confounded with the trunk. 
Cancer, (crab, lobster,) having ten feet ; head 
united to the corslet, forming a shield, covering 
ihe whole anterior part of the body. 
