SPENCER NIAGARA FOSSILS. 563 



IV. 

 " Species having a common avis or rachis, with slender ^ 



alternating branches ; cellules unknown." 5 Thamnograptus. 



V 



"Species having a common axis, more or less frequent-") 

 ly bifurcating with pinnulce closelj and alternately I 

 arranged on the opposite sides; cell-apertures on T ' ograp us. 

 one face of the pinnuhe." j 



VI. 



''A simple flexuous rachis, with slender flexuous flat-"| 

 tened pinnulse arranged in alternate order, at close I 

 and regular intervals, on the two sides. Cell-aper- ^Buthograptus. 

 tures unknown or circular." J 



VII. 



•'Strong stems which are numerously branched; branch- \ 



es and branchlets slender, arranged in whorls ; eel- > 01dhamia( ?). 

 lules undetermined." ) 



VIII. 



Numerous simple short celluliferous stipes originating^ 

 at a common centre and passing through a well- I 

 marked non-celluliferous disc and extending be- ( ^ s P • 

 yond its margin. (Spencer.) j 



List and Range of the Genera fou.nd in the Niagara Group. 



Genera. Range. 



GraptolitJms (Linna-us") Quebec, Hudson River, Clinton. 



Phyllograftua (Hall) Quebec, Niagara(":'). 



Retioliles (Barrande) Quebec, Clinton. 



Dendrograptus (Hall) Potsdam, Quebec, Niagara. 



Callograpttis (Hall) Quebec, Niagara. 



Dictyonema (Hall) \ ^"^^ec, Trenton, Clinton, Niagara, 



c Helderberg; Corniferous, Hamilton. 



Calyptograptusi (Spencer) Hudson(.'),* Niagara. 



Rhizograpttis (Spencer) Niagara. 



Acatit/iograpfus (Spencer) Niagara. 



Inocaulis (Hal!) Niagara. 



Thamnograptus (Hall) Quebec, Hudson, Niagara. 



Ptilograptus (Hall) Quebec, Niagara. 



Cyclograptus (Spencer) Niagara. 



* I obtained a specimen called Inocaulis arbuscula (Ulrich), belonging to Cincinnati 

 Group, which resembles and is probably a species of Calyplograptus. 



