ROUAULT ON TRILOBITES. 39 
relative dimensions, the form and armature, and firmness of substance 
of the buckler, the character of the eyes, size and number of seg- 
ments of the abdomen (thorax, Burm.) ; also the size, form and sub- 
stance of the post-abdomen (caudal shield, Burm.) ; and the author 
deduces from the whole review the conclusion that— 
The five first-named genera have had their organization very perfect, 
and had probably an active life, their protection consisting in nume- 
rous moveable hard segments, with a considerable quantity therefore 
of calcareous matter in them, represented in the fossil state by the 
sulphate of lime and sulphuret of iron. 
The next four he considers of inferior organization, and their pro- 
tection to have consisted in the size of the terminal shields, the crust 
not containing much calcareous matter. 
In the two last the organs of vision were imperfect or absent, the 
protection being afforded by the buckler only, which alone contained 
calcareous matter. 
M. De Verneuil had examined the fossils collected by M. Rouault, 
and the lists from Devonian and Silurian rocks appended to the paper 
derive much additional value from his revision; they are too ex- 
tended for insertion here. 
The characters of a few new species of Trilobites and one or two 
genera are also given (with figures) : 
Calymene Tournemini, very like Calymene Fischeri, Kichw., and 
belonging to the genus Amphion, Pander. 
Phacops Dwardin, allied to P. Murchison, Portlock. 
Polyeres,n.g. From the description this would seem to belong to 
Odontopleura? 
Prionocheilus, n. g. According to De Verneuil this is probably 
identical with Calym. pulchra, Barrande, C. brevicapitata, Portlock. 
Chetrurus Durochert. 
Nileus Beaumontii, allied to N. Armadillo. 
Ogygia Edwardsii, more elliptical than O. Buchit. 
The author in conclusion offers a few observations on the structure 
of the eye; but the structure he describes has been already indicated 
by Prof. Burmeister (Organiz. der Trilobiten) ; the employment of 
the variations, however, as specific characters is new and probably 
will be useful. 
The cornea shows some curious variations in the genus Phacops ; 
in P. macrophthalmus the thickness is such between the lenses, that 
the latter lie in hollows between the meshes which rise above them 
and protect them from abrasion ; in P. Downingie, on the contrary, 
it is a thin film, the lenses themselves projecting a little; m P. lon- 
gicaudatus, again, it is very thick. The size of the lenses, again, is 
greatest in the first of these three, and least in the last,—another 
good specific character. 
(J. W. 8] 
