XVI 



IXTRODUCTJON. 



III. Chronological Distribution. 



Oriskany sandstone. 



In the eastern outcrops of this formation but a single Crustacean species is 



known, the gigantic Homalonotus major, from Ulster county. In the western 



extension of these rocks into the Province of Ontario, are the species 'Phacops 



cristata, Dalmanites (Ilaiismannia) pleuroptyx and Dalmanites (Chasmops) anchiops, 



ail of which occur in the overlying Upper Helderberg limestones, a fact 



which indicates the close alliance of the western Oriskany fauna to the true 



Devonian. 



Upper Helderberg group. 



Cauda-galli grit. 

 No Crustacea have been found in this formation. 



Schoharie grit. 

 The rich Crustacean fauna of these rocks is exclusively trilobitic, and con- 

 Bists of eighteen species from the local development of the formation in eastern 

 New York. These arc : 



Caly ■ ii platys. LicJias (Terataspis) grandis. 



Phacops cristata. Lichas (Conolichas) hispidus. 



Dalmanites (Hdusmannia) concinnus. Proetus Conradi. 



/i. tanites (Coronnra) emarginatus. Proetus angustifrons. 



Dalmanites (Corycephalus) regalis. Proetus Hesione. 



Dalmanites [Chasmops) anchiops. ProHus crassimarginatus. 



Dal tanites (Chasmops) anchiops, var. armatus. Proetus sp. 



DalmaniU (Chasmops) anchiops, var. sobrinus. Phaethonides arenicolus. 



.1. idaspis callicera. Cyphaspis minuscula. 



In addition to these are the species Proetus curvimarginatus and Proi'tus latimar- 

 ginatus, from the sandstone beds at Pendleton, Indiana, which lie at the base of 

 the Corniferous limestone, and contain a fauna closely allied to that of the 

 Schoharie grit in the State of New York. 



Corniferous limestone. 



The greatest numerical development of the Devonian Crustacea, as a whole, 



is found in this extensive formation. The species are, however, mostly 



of Trilobites which here attain their specific and individual culmination, all 



other orders of Crustacea, excepting the Cirripedia being unrepresented. The 



