In this paper are recorded the results of an investigation undertaken at the instance of Dr. A. Smith Woodward for the purpose of ascertaining to what extent the pattern presented by the calcified laminæ of the centrum is of value as an aid to the classification of Elasmobranch fishes, and to the identification of vertebræ found in the fossil state. The subject was dealt with exhaustively in 1879-1885 by Hasse, who, in his monograph ‘Das natürliche System der Elasmobranchier,’ claimed that the differences in the disposition of the calcified laminæ in the various genera and families of Elasmobranchs occur with such constancy and regularity that they may be accepted with confidence as an important factor in taxonomy. During the years, however, that have passed since the publication of this monograph the thesis has come to be looked upon with suspicion, and vertebrate morphologists at the present time do not, as a whole, regard Hasse’s definitions of the Cyclospondyli, Tectospondyli, and Asterospondyli as consistently applicable to the genera and species included by him within those groups. The material studied in the course of the investigation was to a large extent accumulated several years ago (see p. 313), and it was only the superior attraction of
Cephalodiscus
as a subject of research that prevented the work from being brought to an earlier conclusion. The examination of this accumulated material, and of that more recently acquired, was carried on in the Huxley Research Laboratory of the Imperial College of Science during the winter of 1917 and from May, 1919, to May, 1920, and I hereby acknowledge my great indebtedness to Prof. E. W. MacBride and the administrative officers of the College for the facilities offered there for the prosecution of the work. I have further to thank Prof. MacBride for frequent advice and for valuable suggestions made during the progress of the research. My thanks are also due, and are hereby tendered, to Dr. A. Smith Woodward and Mr. C. Tate Began, of the British Museum (Natural History), for many helpful hints and suggestions. Acknowledgments and thanks for material kindly furnished by various donors are recorded on p. 313.
A Monograph on the Development of Elasmobranch Fishes
