xviii INTRODUCTION. 



Of these sped occurs in the Lower Helderberg group, viz.: Dalmanites 



{Hausmannia) pleuroptyx ; three in the Oriskany sandstone, viz. : Phacops cristata, 

 Dalmanites {Hausmannia) pleuroptyx, and Dalmanites (Chasmops) anchiops; and eleven 

 in the Schoharie grit, viz. : 



Liclias (Terataspis) grandis. 

 Liclias (Conolichas) hispidus. 

 /)„/,,, ins crassimarginatus. 



anchiops. Phaithonides arenicolus. 



... n ncldops, var. annatu, Cyphaspis minuscula. 



Hut a single characteristic species of this fauna ranges upward into the Hamil- 

 ton, viz.: Phaithonides gemmcuus. 



Hamilton group. 



Marcellus shales. 



The Trilobites found in these beds all pass upward into the Hamilton shales 



when- thev attain a more perfect development. These are: 



Proetus Ealdt mi mi. 

 Prot tus mat rocepJialus. 

 ' <cs) Bootlii. 



The peculiar character of the sea which deposited these bituminous shales was 

 not favorable to the existence of these animals, and it is only where the deposit 

 becomes calcareous that trilobitic remains are found. In addition to these 

 occurs the earliest known species of the Devonian Phyllocarida, Mesothyra 

 {Dithyrocaris ?) Veneris, and the interesting Cirripede, Protobalanus Hamiltonensis. 



Hamilton shales. 

 In the rich fauna of these beds, the Crustacean element is much more varied 

 than at any other Devonian horizon. The Trilobites have become much fewer 

 in number since the (dose of the Upper Helderberg period, their place being 

 taken by members of other Crustacean orders. The species occurring in the 

 group are as follows: 



Dalm i rites (Cryphwus) PI i 



writes [Crypho us) Boothi. 

 Dalmanites {CryphCBUs) Boothi, var. Callitehs. 

 Dalmanites (Cryphmus) Bairisi. 

 1 Acidaspis Romimgeri. 



