INTRODUCTION. 
xviii 
Of these species one occurs in the Lower Helderberg group, viz.; Dalmanites 
(Ilausmannia) phuroptijx; three in the Oriskany sandstone, viz.; Phacops cristata, 
Dalmanites {Hausmannia) pleuroptyx, and Dalmanites (Chasmops) anchiops; and eleven 
in the Schoharie grit, viz.; 
Calymene 'platus. Lichas ( Teratasiyis) grandis. 
Fhacops oristata. Lichas (Conolichas) Mspidus. 
Baliiianltes ( Hatismaniua) conchinus. Proctus crassimarginatiis. 
Dalmanites {Chasino}^) anchiops. Phaefhonides areyiicolws. 
Dalmanites {Chasmops) anchiops, var. aymatiis. Cyphaspis minuscula. 
Acidaspis calliccna. 
But a single characteristic species of this fauna ranges upward into the Hamil¬ 
ton, viz.; Phaethonides gemmce.us. 
Hamilton group. 
Marcellus shales. 
The Trilobites found in these beds all pass upward into the Hamilton shales 
Avhere they attain a more perfect development. These are: 
Homalonotns Dckayi. Proetus Haldemani. 
Phacops rana. Proetus macrocephalus. 
Dalmanites (Cryphaius) Booihi. 
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 Ilamiltonensis. 
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 close of the Upper Helderberg period, their place being 
taken by members of other Crustacean orders. The species occurring in the 
group are as follows: 
Homalonotns Dekayl. 
Phacops imia. 
Phacops bnfo. 
* Phaco 2 )s Cacapona. 
* Dalmanites {Hausmannia?) Meeki. 
* Dalmanites {Cryphwus) Pleione. 
Dahnanites {Cryphwus) Booihi. 
Dalmanites {Cryphwus) Boothi, var. Callitehs. 
* Dalmanites {Cryphwus) Barrisi. 
* Acidaspis Romingeri. 
