[40] See W.G. Ridewood, Nat. Sci. vol. VIII. 1896, p. 380. Full references are there given to the literature of the subject.
[41] See H. Gadow and E.C. Abbott, Phil. Trans. vol. 186 (1895) B. pp. 163-221.
[42] C. Hasse, Zeitschr. wiss. Zool. LVII. 1893, p. 76.
[43] C. Hasse, Das natürliche System der Elasmobranchier auf Grundlage des Baues und der Entwickelung ihrer Wirbelsäule, Jena, 1879 and 1885, and "Die fossilen Wirbel, Morph. Studien I.-IV.," Morphol. Jahrb. Bd. II., III. and IV. 1876-78.
[44] See H.B. Pollard, Anat. Anz. X. 1894.
[45] T.W. Bridge, "The Cranial Osteology of Amia calva," J. Anat. Physiol. norm. path. 1876, vol. XI. p. 605. R. Shufeldt, "The Osteology of Amia calva," Ann. Rep. of the Commissioner for Fish and Fisheries, Washington, 1885.
[46] A. Smith Woodward, Nat. Sci. vol. I. 1892, p. 28. Further references are here given on the literature of the subject.
[47] C. Gegenbaur, Ueber das Archipterygium, Jena Zeitschr. der Wirbelthiere, 2e Heft, 1873, vol. 7, and Morphol. Jahrb. XXII. 1894, p. 119.
[48] The fins of Ceratodus are very variable, no two being exactly alike. Sometimes even the main axis bifurcates. See W.A. Haswell, Linn. Soc. N. S. Wales, vol. VII. 1882.
[49] Some of these views with regard to the homologies of the parts of the fins are not accepted by all anatomists.