JUL 12 1901 



AETICLE II. 



THE CHRONOLOGICAL DISTRIBUTION OF THE ELASMOBRANCHS. 



J!Y O. P. HAY. 



Bead October 19, 1900. 



In Science, Vol. x, L899, p. 68:>, the writer published a diagram which was designed 

 to represent graphically the chronological distribution of the fossil fishes of North 

 America. Since then it bus appeared that a further analysis of the subject is desir- 

 able; and this, so far as it pertains to the Elasmobranchii, is here attempted. In the 

 former presentation the Permian period was not separated from that of the Coal-meas- 

 ures ; nor were the Mesozoic and Cenozoic ages resolved into their constituent periods. 

 This is here done in a new diagram. Furthermore, the distribution of the fossil Elas- 

 mobrancbs of Europe is displayed, as well as that of those of North America, the dis- 

 tribution of the former by means of the continuous, that of the latter by the beaded 

 li ne. From the estimates and statements here given the " ichthyodorulites " have been 

 excluded, although on account of Onchus the lines have been made to begin with the Upper 

 Silurian. The numbers accompanying the lines show the riumber of species known to 

 exist at the times indicated. It may be explained further that the upright lines, and 

 Q ot the spaces, represent the periods of time. For the data, appertaining to the Euro- 

 pean genera and species discussed in (his paper, I am indebted especially to Mr. A. 8. 

 Woodward's Catalogue of the Fossil Fishes; and this work has also furnished me assist- 

 ance on the American forms. 



An examination of the diagram shows that during the Palseozoic era. North 

 America possessed a greater number of species than did Europe; while, ever since (he 

 Permian period, Europe has considerably surpassed North America. In both North 

 America and Europe 'the culmination of the class was attained during the Subcarbonif- 

 erous period; in both there was a rapid decline in genera and species during the time 

 oi the Coal-measures. This, as regards America, was shown in the earlier published 

 diagram, but the latter obscured one tact which is here strongly brought out, namely, the 



A. P. S. — VOL. XX. I. 



