On the Tertiary Shells of the Amazonfr Valley. 59 form and size were concerned, agreed perfectly with the parasites of Anodotita, but instead of the great number, had only six suckers on each side. Are these to be regarded as a distinct species? I think not. At any rate, we shall do better to regard this peculiarity as a case of atavism, especially as the two species are not widely distant. In any case the mite with five suckers on each side will have made its appearance earlier in the natm-al genealogical tree than that with from thirty to forty. But the form with six suckers is a reversion towards the primary form. VIII. — The Tertiary Shells of the Amazons Valley. By Henky Woodward, F.G.S., F.Z.S., of the British Museum. Of the great river-systems with which explorers have made us acquainted, that of the Amazons is perhaps the most re-markable, as it is also one of the largest in the world. The courses of nearly all the large rivers of our earth lie in a north and south direction ; thfe Amazons, on the contrary, runs nearly west and east. Situated almost beneath the equator, it traverses the southern continent of America from the eastern slopes of the Andes to the North-Atlantic Ocean (nearly fifty degrees) — a distance, computed by its course, of upwards of 4000 miles. Twenty great rivers, all of which are navigable, contribute their waters to its stream, which, under various names, drains considerably more than two millions of square miles of country. It is 40 miles wide where it enters the sea, whilst at 400 miles up stream, to which distance the tide ascends, it is still more than a mile in width*. The stratified sandstones and clays observable in this great valley were attributed by Gardner to the Cretaceous series ; Spix and Martins described them as belonging to the Quadersandstein formation f (Upper Cretaceous). By the earlier observers, according to LyellJ, the stratified portions of this series were supposed to be of marine origin, and were successively referred to the Devonian, Triassic, and Tertiary epochs. Our own countryman, Henry Walter Bates, who devoted eleven years to the exploration of the natural history of this region, has given us most graphic accounts, in ' the Naturalist on the Amazons,' of the scenery, physical features, &c., but does not dwell much upon its geology. It was left to Prof. Agassiz, after his visit to Brazil (1865-* Ansted's Physical Geography, 1867, p. IGO. t Hartt, ' Brazil,' p. 484. % Principles, vol. i. p. 407.
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