I know, he observes, only the tail of this Asaph, but it is so different from that of other trilobites, that I do not hesitate to establish a particular species, upon the consideration of this part alone. Its general form is that of a semi-ellipsis; the middle lobe represents a very slender cone. The arched ribs of the lateral lobes are perfectly distinct and simple. I cannot perceive in them the slightest appearance of bifurcation. This sufficiently characterizes the species. But that which further distinguishes it from the others, are the small, elevated points, scattered, and of course rough (serrés), with which the skin or epidermis is covered, resembling, in this respect, the tail of the _Apus canceriformis_. This fragment of an Asaph is in a homogeneous, compact, blackish limestone, which contains no other kind of petrifaction. I know not where it was found. It is in the cabinet of M. de Drée. On plate 2 of Professor Brongniart's work, he has given figures to illustrate this species; fig. 3 A. represents the whole fragment, and 3 B. two of the ribs of the lateral lobes, magnified to show the arrangement of the tubercles, which are very peculiar. From the above description it will be readily perceived, that the A. Hausmanni comes very near to the A. Laticostatus. There are, however, many striking differences, which will be obvious to those who compare our cast with the figures of Brongniart. The shape of the ribs, and the tubercles upon them; the form of the middle lobe and of the interstices between the articulations, are all peculiar to each. The elongation of the tail in our species is alone sufficient to distinguish it. We have always been doubtful whether the minute granulations on our species were not produced by the sandstone in which it is petrified. Upon what authority the A. Hausmanni has been considered as a species belonging to the United States we cannot determine. In the valuable and extensive cabinet of trilobites belonging to the Albany Institute, there are a number of specimens labelled with this name by Professor A. Eaton. If we mistake not, he mentioned to us that similar fragments of this fossil were sent by him to Brongniart, who, we understand, is the author of the list of trilobites found in the manual of De la Beche. The specimens which have been examined, both in the cabinet of Professor Eaton, and in that of the Albany Institute, are certainly not identical with the figures or descriptions published of the A. Hausmanni. Professor Eaton, in his Geological Text Book, at page 31, thus describes his A. Hausmanni:--"Tail rounded, and forming the middle of a circular arc whose centre is in the fore abdomen, near the head; covering tubercled or spined. Found in coral rag on the south shore of Lake Erie. Also, in its underlaying grit slate on the Helderberg." Some other trilobites mentioned in De la Beche's list as occurring in the United States, we have not been so fortunate as to meet.