380 
CLASS CRUSTACEA. 
or lobes, and from thence the origin of the denomination 
trilobites. With some scientific men, these are called ento- 
mostracites . The squillse, various amphipod and isopod 
Crustacea, have also several of their segments divided into 
three, by two sunk and longitudinal lines ; but those lines are 
more approached to the edges, and do not form deep furrows. 
It would seem that in many trilobites, and particularly in 
the Asaphi, that the body is composed, (the buckler not com- 
■prehended) of a dozen segments, very much detached over 
the sides, and of another forming the post-abdomen, or a tail, 
triangular or semi-lunar, presenting only superficial divisions, 
and which do not cut its edges. In the paradoxides, on the 
contrary, the lateral lobes are terminated by sharp and very 
distinct elongations, of which we reckon nearly twenty-two. 
A species of trilobite mentioned by Count Razoumowsky, in 
a memoir on the fossils, and which he presumes ought to con- 
stitute a new genus, is, in this particular, very remarkable. 
Its lateral lobes form sorts of strips, very long, and going into 
a point. The feet of the nymphs of the gnats are in the form 
of elongated, flatted laminte, without articulations, terminated 
by filaments, and folded back upon the sides. They are in a 
rudimentary state, and may be analogous to the lateral divi- 
sion of this species of trilobite, which is neighbouring to the 
paradoxides. 
The genus Agnostus, Brogn ., is the only one whose body 
is semi-circular or reniform. In all the other genera it is oval 
or elliptic, and presents the general characters which we have 
above indicated. 
Calymene, Brogn is distinguished from all the other 
trilobites, by the faculty of being able to contract the body 
into a ball, and in the same manner as splieroma, the arma- 
dillo, the glomeris, that is, by approximating together, un- 
derneath, the two extremities of the body. The buckler, as 
