The tertiary deposits of the east coast of Patagonia, which yielded to the researches of Mr. Darwin and Admiral Sulivan such interesting and aberrant mammals as
Macrauchenia
,
Nesodon
, and
Toxodon
, have again disclosed a new and remarkable form of extinct animal life. The evidence upon which the existence of this new genus rests consists of a nearly complete set of teeth and some fragments of bone, discovered on the bank of the River Gallegos, by Dr. Robert O. Cunningham, Naturalist to H.M.S. ‘Nassau.’ during the voyage undertaken for the purpose of surveying in the Strait of Magellan and the west coast of Patagonia in the years 1866, 1867, 1868, and 1869. The spot was visited in conformity with instructions received before leaving England, “to institute a search for a deposit of fossil bones discovered by Admiral Sulivan and the present Hydrographer of the Navy, Rear-Admiral G. H. Richards, about twenty years previously, and which Mr. Darwin, Professor Huxley, and other distinguished naturalists were anxious should be carefully examined”. The conditions under which the specimens were found will be best understood from the following additional extract from Dr. Cunningham’s narrative. “Accordingly, joined by the steamer, which again took us in tow, we proceeded onwards till we arrived opposite the first deposit of fallen blocks at the foot of the cliffs. The cutter was then anchored in the stream, while we pulled in towards the shore in the galley till she grounded, when we landed, armed with picks and geological hammers for our work. After examining the first accumulation of blocks, and finding in the soft yellow sandstone of which certain of them were composed some small fragments of bone, we proceeded to walk along the beach, carefully examining the surface of the cliffs and the piles of fragments which occurred here and there at their base. The height of the cliffs varied considerably, and the highest portions, averaging about 200 feet, extended for a distance of about ten miles, and were evidently undergoing a rapid process of disintegration, a perpetual shower of small pieces descending in many places, and numerous large masses being in process of detaching themselves from the parent bed. They were principally composed of strata of hard clay (sometimes almost homogeneous in its texture, and at others containing numerous rounded boulders) ; soft yellow sandstone ; sandstone abounding in hard concretions; and, lastly, a kind of conglomerate, resembling solidified, rather fine gravel. The lowermost strata, as a rule, were formed of the sand stone with concretions; the middle, of the soft yellow sandstone, which alone appeared to contain organic remains; and the upper, of the gravelly conglomerate and hard clay. Nearly the whole of the lower portion of the cliffs, as well as all the principal deposits of fallen blocks, were examined by us in the course of the walk, and we met with numerous small fragments of bone ; but very few specimens of any size or value occurred, and the generality of these were in such a state of decay as to crumble to pieces when we attempted, although with the utmost amount of care that we could bestow, to remove them from the surrounding mass. To add to this, the matrix in which they were imbedded was so exceedingly soft as not to permit of being split in any given direction. The first fossil of any size observed by us was a long bone, partially protruding from a mass, and dissolved into fragments in the course of my attempts to remove it. At some distance from this a portion of what appeared to be the scapula of a small quadruped, with some vertebrse, occurred; and further on one of the party (Mr. Vereker) directed my attention to a black piece of bone projecting from one side of a large block near its centre. This, which was carefully removed at the expense of a large amount of labour, with a considerable amount of the matrix surrounding it, by three of the officers, to whose zeal in rendering me most valuable assistance in my work I shall ever feel deeply indebted, afterwards proved to be a most valuable specimen for on carefully removing more of the matrix when we returned to the ship, I found that it was the cranium of a quadruped of considerable size, with the dentition of both upper and lower jaws nearly complete. As no other specimens of importance were discovered, we reembarked towards the close of the afternoon.
Diversity of benthic marine mollusks of the Strait of Magellan, Chile (Polyplacophora, Gastropoda, Bivalvia): a historical review of natural history
