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Above the upper beds of the Great Conglomerate, at dis-tances varying from forty to a hundred and sixty feet, thefishes of the Lower Old Red Sandstone appear,—curious, asthe most ancient ganoids known to the geologist, and fur-ther, from the circumstance that, while the still older placoidsof the Upper Silurian system exist merely as detached teeth,spines, and shagreen points, these Old Red fishes exhibit inthe better specimens the entire outline of the original ani-mals, with not a few of their anatomical peculiarities. It isfrom this formation that our knowledge of the oldest skulls,of the oldest vertebral columns, and of the oldest pelvic andthoracic arches, anywhere preserved, is to be derived. Withthe fish we sometimes find associated, though not often, speci-mens illustrative of what seems to be our most ancient ter-restrial Flora,—club-mosses,—reed-like casts and impressions,streaked longitudinally, like the interior of the calamite, butapparently without joints,—what appear to be ferns,—and,in at least one unique specimen, a true wood of the arauca-rian family,—the oldest which has yet presented its structureto the microscope. In some localities, such as Cromarty,Thurso , and perhaps Moray, the various ichthyic species ofthe formation seem to have been pretty nearly ascertainedand collected : for several years I have not succeeded in dis-interring from the several Cromarty deposits a single newspecies ; and my friend Mr Dick, though permanently resi-dent on the spot, has had a similar experience at Thurso .Species of the rarer kinds may, however, long elude very as-siduous search, and yet turn up at last; and in the courseof the present twelvemonth I have received from a tract ofshore near Cromarty, which I have walked over many hun-dred times, an ichthyic species,—the Diplacanthus crassispi-nus ,—of which my collection had possessed no previous speci-men. I owe it to the kindness of Miss Catherine Allardyce^—a lady who, to a minute knowledge of not a few other