Since the publication of Agassiz' ‘Poissons Fossiles’ only one addition, that we are aware of, has been made to our knowledge of this interesting genus of fishes,—certainly, at least, in respect to British geology. In 1845 Sir Philip Egerton described, before the Geological Society, a large jaw, or rather mouth of teeth, of a fish of this kind, found by Captain Ibbetson in the Isle of Wight, and named by Sir Philip Hylodus bassanus.

This species has been assigned to the Lower Greensand, in Morris's Catalogue, but the bed seems, from Sir Philip's statement, to be in a dubious position, for he speaks of it only as “near the junction of the Lower Greensand and Wealden,” and says the specimen was sent to him “in the hopes it might tend to show to which of the two formations its bed should be assigned,”—a question he further declines to answer, as “the evidence it affords on this question is neither direct nor conclusive, inasmuch as it is an undescribed species; and consequently any deductions beyond those based upon general affinities would be unwarrantable.” Sir Philip adds, however, further on: “The geological inferences afforded by the specimen are briefly told. The species is new. The genus is undoubtedly Hybodus. This genus attains its maximum expansion in the Oolitic series, but it ranges from the Muschelkalk to the Chalk inclusive.

The following interesting letter by Professor Hall (31st Oct. 1862), “On a New Crustacean, from the Potsdam Sandstone,” was published in the December number of the ‘Canadian Naturalist.’

I have been much interested in reading your observations upon the tracks of Limulus in sand, and comparisons with the tracks in the Potsdam Sandstone; more especially as these observations connect themselves in a remarkable manner with a recent discovery of my own; and a question may arise as to whether you have described an animal which I have found, or I have found the animal corresponding to your description. I will leave you and the scientific world to judge of the facts. However, after what you have written, I cannot now publish what I communicated to the Albany Institute last winter, without referring to your paper; and in the meantime you may lay this note before the Montreal Natural History Society, and publish it, or such parts of it, as you please.

In February last, I communicated to the Albany Institute a notice of a new crustacean from the Potsdam Sandstone of Wisconsin, and subsequently I sent a drawing of the same to M. Barrande. In 1855, I obtained from the Potsdam Sandstone of the Upper Mississippi River, a fragment of what appeared to be a spine of a crustacean, of very remarkable and peculiar structure, reminding one of that bone; and which might at one time, before we had accustomed ourselves to limit the geological range of fishes, have been taken for an ichthyic remain.