XX PROOFS, ILLUSTRATIONS, AUTHORITIES, ETC. 



equally fluviatile and terrestrial ; and among these the fluviatile 

 ranking immediately above the marine, and the terrestrial ranking 

 highest." Sillimans Journal, May, 1850. 



Cephalopoda. The first division which Professor Owen has made 

 in the Cephalopoda is into Tetrabranchiata and Dibranchiata (having 

 four branchiae and two branchiae). The Tetrabranchiata are placed 

 by him lowest, by virtue of the law "that increased number, irre- 

 spective of co-relative structure in an organ of the animal body, is 

 ever a mark of inferiority." Lectures on the Invertebrate Animals. 



The earliest cephalopods were tetrabranchiate. None of the 

 dibranchiate appear till the Lias, the commencement of the Secon- 

 dary Formations. 



Among the tetrabranchiates, which are the earliest ? 



In the remarkable example of the Silurian formation, which has 

 been so well explored by M. Barrande, in Bohemia, after one series 

 in which there are trilobites, cystideas, etc., there is another, contain- 

 ing, with these and other fossils, fragments of orthoceratites, being 

 the first appearance of the cephalopodous order. In the next stage 

 again are an enormous variety of the same genus, from 95 to 100 

 species, together with various nautili and lituites. In the same 

 formation in the state of New York, after a fossiliferous series 

 without any appearance of the cephalopoda, there is one (Calciferous 

 Sandstone), containing some small orthoceratites; then another 

 (Chazy Limestone), containing some examples of the same fossil, 

 but much larger; then still another, containing orthoceratites eight 

 or ten feet long, etc. In the various examples of the Silurian for- 

 mation in the British Islands, the order of the appearance of the 

 orthoceratites is nearly the same. " The Orthoceratites, apparently 

 the first, as it is the simplest, form of the multilocular shell," says 

 Professor Ansted. 



And how, after this, proceeds the march of cephalopodous life ? 

 Agassiz answers " The Orthocera of the oldest periods precede the 

 curved Lituites, which in their turn are followed b^vthecircumvolute 

 Nautilus" " Here we have," he says, " a natural gradation of a 

 series of progressive types." Address to Amer. Assoc.for Advan. 

 of Science, 1849. This may be stated more in detail. " The cepha- 

 lopodous animals, whose remains are most abundantly distributed 

 in the older Palaeozoic rocks, had their numerous chambers not 

 twisted round a central axis, as in the nautilus, but placed one over 

 another in a position more or less approaching the vertical ; and not 

 less than eighty species of these have been determined. The straight 

 form of the shell is best known by the generic name Orthoceratite ; 

 but the names Lituite, Phragmoceratite, Cyrthoceratite, and Gom- 

 phoceras are also applied to distinguish differences of form, chiefly 

 marked by the axis of the chambers being more or less curved ; the 

 chambers of none of them, however, being twisted into a complete 

 spiral." Ansted : Introduction to Geology. 



Dr. Carpenter says " Among the higher mollusca, we find that 



