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There can be no doubt, on the other hand, that conchologists have occasionally rejected from the Red and Norwich Crags, as derivative, shells which really belonged to the seas of those periods, because they were extinct or unknown as living, which in their eyes afforded sufficient ground for suspecting them to be intruders.
As the Dreissena is believed by conchologists to have been introduced into Western Europe in very modern times, brought with foreign timber in the holds of vessels from the rivers flowing into the Black Sea, the layer of sand containing it in the Haarlem lake is probably not more than a hundred years old.
It has been very generally admitted by conchologists that out of a hundred species of this tribe occurring fossil in the Upper Chalk one, and one only, Terebratulina striata, is still living, being thought to be identical with Terebratula caput-serpentis.
Some experienced conchologists are now sinking many of the very fine species of D'Orbigny and others into the rank of varieties; and on this view we do find the kind of evidence of change which on my theory we ought to find.
Some experienced conchologists are now sinking many of the very fine species of D'Orbigny and others into the rank of varieties; and on this view we do find the kind of evidence of change which on the theory we ought to find.
But still so it is that tours in search of the picturesque are peculiarly apt to break up in quarrels. Perhaps on the same principle which has caused a fact generally noticed, viz. that conchologists, butterfly-fanciers, &c., are unusually prone to commit felonies, because too little of a human interest circulates through their arid pursuits.
The Chambered Nautilus is familiar to all, since, from the exquisite beauty of its shell, it is especially sought for by conchologists; but it is nevertheless not so common in our days as the Squids and Cuttle-Fishes, which are the most numerous modern representatives of the class.
It is enough at present to remark that the character of the Eocene fauna, as contrasted with that of the antecedent Secondary formations, wears a very modern aspect, and that some able living conchologists still maintain that there are Eocene shells not specifically distinguishable from those now extant; though they may be fewer in number than was supposed in 1833.
The terrestrial shells are all univalves. Many fossil species formerly referred to this genus, and which have been met with chiefly in marine formations, are now considered by conchologists to belong to Natica and other marine genera. Pleurotoma exorta, Brand. Upper and Middle Eocene. Ancillaria subulata, Sowerby. Barton clay.
We shall, perhaps, best perceive the improbability of our being enabled to connect species by numerous, fine, intermediate, fossil links, by asking ourselves whether, for instance, geologists at some future period will be able to prove, that our different breeds of cattle, sheep, horses, and dogs have descended from a single stock or from several aboriginal stocks; or, again, whether certain sea-shells inhabiting the shores of North America, which are ranked by some conchologists as distinct species from their European representatives, and by other conchologists as only varieties, are really varieties or are, as it is called, specifically distinct.
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