Fillet nearly straight in front of the middle lobe of the head, punctures of the fillet scattered irregularly, without any alternating ridges; head compressed, covered with scattered punctures, having its side lobes much smaller than the middle one; middle lobe with straight sides, giving it somewhat the form of a parallelogram. Found in third grauwacke,[47] or grit slate in Coeymans, sixteen miles south-west of Albany. I have the head of one before me two and a half inches broad, and one and a half long. The whole of the animal must have been six or seven inches in length. [Footnote 47: In a manuscript note, Professor Eaton states that the third grauwacke, or grit slate of Coeymans, "_alternates_ with the underlaying cherty lime rock." This opinion some of our geological friends, familiar with the formation at Coeymans, and with the Professor's nomenclature of rocks, have called in question.] The above account is copied from the "Text Book." Mr. Eaton was kind enough to lend me the only specimen of this curious fossil remain, which has yet been found; from which his description was taken, and of which our cast is an exact copy. His generic characters do not in our opinion at all apply to this fragment. Nothing but the head of this singular trilobite remains, and it is doubtful whether what is said to be the punctured fillet, "nearly straight in _front_ of the middle lobe," be not the commencement of the articulations of the abdomen. The whole fragment looks very much like the head of some large Asaph or Ogygia. Genus Brongniatia. _Eaton._ Professor Eaton has proposed the name Brongniatia (Brongniartia?) for a genus of trilobites, which we think he has not defined with sufficient accuracy to be of any practical use. The _Isotelus gigas_ of Dr. Dekay, which has been for a long time so well established, is here ranked merely as a species under the name of B. isotela. The relic which we described before the Geological Text Book appeared as the _Triarthrus Beckii_, forms the species B. carcinodea--and the trilobite which is supposed to be the Asaphus platycephalus of Stokes, is the only other species mentioned. The A. platycephalus,[48] we know to be identical with the I. gigas, and as the animal remain described by Mr. Eaton is entirely different from Dr. Dekay's fine species, we subjoin the account given in the "Text Book." [Footnote 48: For a figure and description of the Asaphus Platycephalus, by Mr. Stokes, see Transactions of the Geological Society. Second Series, vol. i.] Genus Brongniatia--Fore abdomen always, and post abdomen in some cases, longitudinally divided into three lobes, by regular series of undulations traversing the joints, without grooves; articulations of the side lobes being manifest continuations of those of the middle lobe, and consequently, agreeing in number. Brongniatia Platycephala. _Eaton._