_Body_, very much depressed, and slightly tapering.
_Buckler_, scarcely trilobate; cheeks large, flat, with small remote
oculiform tubercles; posterior angle of the buckler spinous.
_Abdomen_, with twelve articulations.
_Tail_, rounded at the end, but terminating on each side with two
slightly curved spines.
The name of this genus is derived from the remarkable spinous
projections from the caudal end; this peculiar organization separates
it widely from the other genera. The _Paradoxides Spinulosus_ of
Wahlenberg, which is supposed to be the old _Entomolithus Paradoxus_
of Linné, the fossil, with which all the trilobites were for a long
time confounded, has not only projecting spines from the tail, but from
all the costal arches of the lateral lobes. The presence of eyes or of
oculiferous tubercles in the _Ceraurus_, would alone be sufficient to
separate it from the genus to which that interesting fossil belongs. In
the eighth volume of Annales des Sciences Naturelles, Count Rasoumowsky
has figured and described the fragment of a very curious relic, which
seems to be an intermediate link between our genus and paradoxides; in
addition to a number of filamentous elongations of the costal arches, a
curved spine seems to project from the end of the tail, as in the _A.
limulurus_. No name is given to this trilobite, which appears to have
been found on the banks of the Yaousa, near Moscow, where it occurs in
black, coarse, argillaceous schistus. The Ceraurus is probably a very
rare animal remain, as we have only met with it, in the unrivalled
cabinet of trilobites belonging to the Albany Institute.
Ceraurus Pleurexanthemus. _Green._ Cast No. 33. Fig. 10.
Clypeo postice arcuato, angulo externo in mucronem valde producto;
oculis minimis remotis, postabdomine in spinam arcuatam acutam
utrinque extenso.
The exact contour of this species cannot be perfectly ascertained from
our specimen; it seems, however, to have been lunate. The horns of the
crescent which form the posterior angles, are very distinct, and they
project like curved spines, some distance on each side of the head.
The middle lobe or front is faintly scalloped on each side along the
cheeks. The cheeks are rather large, and are furnished with two small
oculiform tubercles, very remote from each other, and quite near to
the anterior portion of the buckler. The abdomen is composed of twelve
articulations. The lateral lobes of the abdomen are flat, and each of
the ribs, at about half their extent, is marked on the upper surface,
with an elevated pimple. These little pustules are nearly on a line
with the oculiferous tubercles of the buckler, and present two parallel
ranges down the body, one on each side of the middle lobe, and are
terminated by a curved spine, which projects to some distance beyond
the tail of the animal. Length one inch and a fourth.
This remarkable organic relic was found near Newport, in the State of
New York. It is embedded in black limestone shale, and so exceedingly
depressed is this animal, that a very thin lamen of the slate removed
from the surface would destroy every vestige of its appearance. I am
indebted to my early friend, Professor T. R. Beck, for the use of this
valuable petrifaction, which now belongs to the cabinet of the Albany
Institute.