v j # PREFACE. 



There are Black-river limestone species, viz., Columnaria alveolata, 

 and the remarkable cephalopod, Gonioceras anceps, of Hall. Of 

 Trenton species, we have in abundance the Strophomena Jilitexta, 

 Pentamerus (atrypa) hemiplicatus and Atrijpa increbescens, Murchisonia 

 gracilis and M. bicincta, Cyrtoceras annulalum and C. lamellosum of Hall 

 (C. BilUno-sii of this Decade), Orthoceras arcuoliratum, bilineatum and 

 laqueatum of Hall, together with Ormoceras tcmujihim, a fossil common 

 to both the Trenton and Black-river limestones. Schizocrinw nodosus 

 is the common Crinoid, and species of Petraia {Streptelasma), with 

 Favosites hjcoperdon, go to swell the list of Trenton species. Lastly, 

 there is the characteristic Asaphus gigas, so that the parallel is 

 complete. 



J. W. SALTER, 



