This fossil was presented to me some time since by Thomas P. Johnson, Esq., who mentioned that it was found in New Jersey, but that he could not learn its precise locality. Near Patterson, in that State, some trilobites have been discovered--perhaps the C. Bufo may have been derived from that locality. It is composed of a dark greyish limestone, easily cut with a knife. Calymene Bufo. Variety, Rana. Cast Nos. 11 & 12. This fine specimen differs from the one above described, in having the front of the buckler rather smaller, and of a different contour. The whole of the shell is also covered with granulations, which only appear on the head of the other; this, however, may be only an imperfection in the specimens in our cabinet. I am indebted to the Albany Institute for the originals of the models Nos. 11 & 12. They were found at Seneca, Ontario County, New York, in dark, slaty limestone, which also contains cubical crystals of iron pyrites. A fortunate blow of the hammer has fractured the rock which contains this trilobite, so neatly, as to present us at the same time with the petrified animal in an almost perfect state, and also with the mould or matrix in which it was imbedded. This arrangement is beautifully illustrated by our models. Genus Asaphus. _Brongniart._ This genus derives its name from the Greek word Ασαφης--obscure. It embraces perhaps more species than any other genus of the family of trilobites. About twenty have already been discovered. Most of them are very characteristic and can easily be determined, but as the genus Asaphus, is intermediate between Calymene and Ogygia, it is sometimes a little difficult to decide the genus to which the inosculating species on each side, belongs. In general, the Asaphs may be known by the body being very much depressed, and by the membranaceous development, which extends beyond the lateral lobes. The middle lobe of the abdomen, is rarely more than one-fifth the width of the body. As the abdomen and tail of the Asaph are the only portions of the animal commonly found entire, the distinctive characters of the genus above given, may generally be ascertained. Professor Brongniart remarks, that the ribs of the _Asaph_, which correspond in number and position to the articulations of the middle lobe, "are sometimes simple or undivided, at least in the post abdomen, but that they are always bifurcated in the _Calymene_" As far as our observations have extended, these remarks do not apply either in the one case or the other. The head or buckler of the _Asaph_, is not so deeply divided into three lobes as the _Calymene_; they are, however, quite distinct. The oculiferous tubercles are in some species exceedingly well marked by a reticulated structure.