OBSCURE NATURE OF TRILOBIIES. 391 
attracted attention, from their strange pecu- 
liarities of configuration. M. Brongniart, in his 
valuable History of Trilobites, 1822, enumerated 
five genera, * and seventeen species ; other writers 
(Dalman, Wahlenberg, Dekay, and Green,) have 
added ^ve more genera, and extended the number 
of species to fifty-two ; examples of four of these 
genera are given in Plate 46. Fossils of this 
family were long confounded with Insects, under 
thenameofEntomolithusparadoxus ; after many 
disputes respecting their true nature, their place 
has now been fixed in a separate section of the 
class Crustaceans, and although the entire family 
appears to have been annihilated at so early a 
period as the termination of the Carboniferous 
strata, they nevertheless present analogies of 
structure, which place them in near approxima- 
tion to the inhabitants of the existing seas.f 
The anterior segment of the Trilobites (PI. 46, 
Si, passim,) is composed of a large semi-circular, 
or crescent-shaped shield, succeeded by an ab- 
domen, or body (c), composed of numerous seg- 
ments folding over each other, like those in a 
Lobster's tail, and generally divided by two 
* The names of these Genera are Calymene, Asaphus, Ogyges, 
Paradoxus, and Agnostus. Some of these terms are devised ex- 
pressly to denote the obscure nature of the bodies to which they 
are attached ; e. g. Asaphus, from ao-a0/)c, obscure ; Calymene, 
from KSKciXvpfievi], concealed ; Trapado'^ogy wonderful ; ayyojarog, 
unknown. 
t See M. Audouin's Recherches sur les Rapports naturels qui 
existent entre les Trilobites et les Animaux articules. 
