COliRELATION OF THE VERTEBRATE FAUNA. 165 



Notes on tJu ichthyic Remains. — Fishes have been found in the Ludlow 



rocks of the Silurian of England and in the Bloomfield sandstone of 

 Pennsylvania in America, a horizon of the upper portion of the Onon- 

 daga salt group. Professor E. W. Claypole lias also described certain 

 minute spines which he considered might belong to an elasmobranch fish 

 that he found in the Clinton terrane* The evidence, however, is not 

 conclusive, as they may belong to some crustacean. 



It is to he noted that the middle Silurian forms thus far found be- 

 long to the two families Pteraspididse and Cephalaspididse, and that no 

 representative of the great placoderms of the Devonian has been found 

 in the true Silurian. In strong contrast to this the ichthyic fauna of the 

 Harding sandstone appears to contain a characteristic representative of 

 the Placodermata and Crossopterygea "I' the Devonian, and what appears 

 to he a type of the Chimseroidae. Serious objection will undoubtedly 

 he made to the classification, as it is based entirely upon the characters 

 of the dermal plates and scales. These, however, are so pronounce:! 

 that the classification is tentatively adopted. The vertical range of tin' 

 ichthyic fauna is extended downward from the middle ( Upper) Silurian to 

 the base of the Lower Silurian (Ordovician), and the conclusion is reached 

 that the differentiation of vertebrates and invertebrates must have begun 

 in ( 'amhrian time. 



Pending the investigation of the beds containing the fish remains and 

 the collection of more material, it is not desirable to illustrate the inverte- 

 brate fauna or to do more than outline the characters of the fragmentary 

 fish remains. For convenience of reference to the latter, names are applied 

 to three of the most marked forms and illustrations are given of typical 

 fragments of these forms. The classification is tentative. 



Since some doubt was expressed, during the discussion, as to the true 

 zoologic character of the dermal plate-, microscopic sections were made 

 of the tuberculated Asterolepis-Yike forms. These showed microscopic 

 characters much like those found in the Devonian Asterolepis, and Dr. 

 Otto -lack el kindly offered to make a few sketches and write ;i brief note 

 upon them.f 



Descriptions ok the echthyic Fauna. 

 CHIMjEROIDEA. 



DICTYOKHABDUS PRISCUS. N. (JEN., V SP. 



This genus and species is based on a calcified chorda] sheath that has 

 some of the structural characters of the chorda! -heath of Chi nitrra mon- 



*Quurt. Jour. '■•'•! 801 I Ion, \..l 11, 188ii p 1- 



1- 11.. i.- i~ nppptuli •! 1- 1 1 • ' 11 "l l'i .l:i.-K.'l- .li-. 11--1..1, « - 1 ■ LU8 170). 



