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Published online by Cambridge University Press: 01 May 2009
On first thoughts, it may seems that the lowest group of vertebrates, of all the divisions comprised in the animal kingdom, might be most easily described, and its zoological limits defined; but, on examination, the fishes prove to be most curiously linked to the invertebrata below and the amphibian reptiles above. In fact, it is not easy to draw the lines positively between them, and to say where the true vertebrates begin, or where the piscine characters are merged in the reptilian. It is proposed to refer to some of the most aberrant forms of living fish and their fossil affinities; then, briefly passing in review the distribution of the various families in geological time, to see how far descent with modification is traceable in this class of vertebrates.
page 209 note 2 Anatomy of Vertebrates, vol. i.
page 209 note 3 Preliminary Note on the Structure of the Skull, and Brain, in Amphioxus lanceolatus, Proceedings of the Royal Society, 1874, No. 157, 12.Google Scholar
page 209 note 4 Transactions of the Royal Society of Edinburgh, vol. xv. pl. 11, p. 259.Google Scholar
page 210 note 1 Trans, of the Linnsean Society, vol. xviii.
page 210 note 2 A specimen of L. annectens has been on exhibition in the entrance hall of the Brighton Aquarium for more than two years. It is kept at a regular temperature of 70°, and is in a very thriving condition, having grown several inches since it has been in the institution, and thickened proportionately. The animal generally lies quietly at the bottom of its tank, rising occasionally to the surface to take in air. It is fed three times weekly on small pieces of raw beef, which it can be observed to eat in a very unusual manner. When the food is thrown in, the mud-fish stretches itself leisurely and seizes it, as it comes within reach, between its sharply formed vomerine teeth. After masticating it slowly, it throws it out with a quick jerk, and, commencing at the other end, repeats the manœuvre; it then again rejects it, and subjects it to a third process of mastication before finally swallowing it.
page 211 note 1 Ceratodus Phillipsi, Ag., Great Oolite, Mantell Coll., British museum.
page 211 note 2 Transactions of the Royal Society, 1871.
page 209 note 3 Proceedings Zoological Society, 1876, part i. June.
1 ProfNewberry, J. S. (vol. ii. Palaeontology of Ohio, p. 63, pl. 58, fig. 18Google Scholar) recognizes in his new genus Heliodus, occurring in the Upper Chemung group of the American Devonian, the most gigantic member of the family of dipterine ganoids to which Ceratodus, Ctenodus, and Dipterus belong. The teeth resemble in microscopic structure those of Dipterus, and in general shape those of Ctenodus. The upper palatal ones differ, however, from those of all other known dipnoids in being united “in the form of a fully-opened fan.” He is also of opinion that the Palœdaphus insignis of Van Beneden and de Koninck, from the Carboniferous strata of Belgium, is not generically identical with the P. Devoniensis, of the same authors, and while admitting that the former is really a Plagiostome, considers that the latter should be associated with his new dipterine genus under the designation of Heliodus Devoniensis.
1 Euc. Brit., vol. xvii., part i., 1859, art. Palæontology.Google Scholar
page 209 note 1 Two species, namely, Amia scutata and A. dictyocephala Cope, are referred Prof. E. D. Cope (in the Bull, of the United States Geol. and Geog. Survey, No. 1. 2nd series, 1875) to the genus Amia. They are recorded as occurring in the Tertiary Shales of South Park; apparently a freshwater deposit of later Tertiary age.
page 209 note 2 Decade x. of the Memoirs of the Geological Survey, 1861 (Classification of Devonian Fish).
page 209 note 3 In the memoir on Tristichopterus alatus, Eg. (Trans. Roy. Soc. Edinburgh, vol. 27, 1875)Google Scholar, Dr. Traquair follows Dr. Günther in associating the Clenodipterini of Huxley (Ctenodus, Dipterus) with the Dipnoi, but retains the Phaneropleuridœ as a sixth family of Crossopterygian ganoids, sub-dividing the remaining families thus: 1. Polypteridæ; 2. Cœlacanthodæ; 3. Rhombodipteridæ, sub-fam. Glyptolœmini (Glyptulœmus, etc.), Saurodipterini (Osteolepis, Diptopterus); 4. Cyclodipteridœ (Tristichopterus, etc.); 5. Holoptychidæ (Holoptychius, etc.); 6. Phaneropleuridæ (Phaneropleuron, Uronemus). In the memoir on British Carboniferous Ganoids by the same author, published in the vol. of the Pal. Soc. for 1877, the Palæoniscidæ are raised to the rank of a distinct family, and removed from the sub-order Lepidosteoidæ into that of the Acipenseroidei. The Dipnoi are retained as a separate order, and the following classification is proposed for the order Ganoidei.
