XVIU LIFE AND WOEKS OF COPE. 



ing the bearing of the foregoing facts upon published 

 schemes of classification of the Elasmobranchii, the first 

 point to be considered is the validity of Professor Cope's 

 division of the subclass into the two orders Ichthyotomi and 

 Selachii. If the characters of the dentition are of any sys- 

 tematic importance — and when genera of equivalent age 

 are under comparison we believe they are — there can be no 

 hesitation in associating the European and later Palseozoic 

 Pleuracanths with the skulls of the so-called Didymodus, 

 Cope, from the Permian of Texas. (Catalogue, Pt. I., p. 

 xxiii.) 



The order Ichthyotomi being firmly established in 1889, 

 Cope proposed another great suborder, Ostracodermi, to 

 include the peculiar armored fishes without lateral fins, but 

 with jointed appendages apparently articulated with the 

 head plates. Of these Smith Woodward speaks as follows : 

 "A large number of these are still problematical, and it has 

 thus been deemed convenient to treat next in order the 

 great extinct group of Chordate animals to which Professor 

 Cope has applied the name of Ostracodermi. These pertain 

 either to the Class Pisces or to some lower denomination 

 yet to be determined. (Catalogue, Pt. II., p. xvii.) The 

 name Ostracodermi, is preferred for this subclass, because 

 Professor Cope seems to be the only naturalist who has 

 hitherto ventured to remove the Coccostean fishes far from 

 the order that comprises the Asterolepidss." (Catalogue, Pt. 

 II., p. xviii.) 



For the most abstruse problems Cope had an invariable 

 resource of working hypotheses. Thus, the curious fish- 

 like Bothriolepis he compared to the armored Ascidian, 

 basing this surprising view upon the remarkable similarity 

 in the arrangement of plates, arguing that it was reason- 

 able to expect in the early period of Bothriolepis, that back- 

 boned creatures should have been built upon the plan of 

 Ascidian tadpoles. 



