XVI 
INTRODUCTION. 
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 {jUausmannia) pleuroptyx and Dalmanites (Chasmops) anchiops, 
all 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¬ 
sists of eighteen species from the local development of the formation in eastern 
New York. These are : 
Calyrnene platys. 
Phacops cristata. 
Dalmanites {Hausmannia) concinnus. 
Dalmanites {Coronnra) emarghiatus. 
Dalmanites (Corycephahis) regalis. 
Dalmanites {Chasmops) anchiops. 
Dalmanites (Chasmops) anchiops, var. armatus. 
Dalmanites (Chasmops) anchiops, vai'. sohrinus. 
Aeidaspis callicera. 
Lichas ( Teratasjns) grandis. 
Lichas (Conolichas) Impidus. 
Prolitus Conradi. 
Proetus august ifrons. 
Proetus Hesione. 
Prolitus crassimarginatus. 
Proetus sp. 
Phaethonides arenicolus. 
Cyphaspis mimiscula. 
In addition to these are the species Prollus curvimarginatus and Proetus 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 
