SPENCER NIAGAUA FOSSILS. 589 



In general form this species differs from /. pluniulosus in that 

 the branches ai^e more slender, and rise regularly and more abun- 

 dantly from the sides of the main stipes, which radiate from a 

 common origin and do not consist of groups of individual fronds. 

 The radicle appears to have been attached to some rocky surface 

 in the sea, and not to have grown on some muddy bottom. The 

 cell-bearing stipes appear to have had a common canal, through 

 the centre of which was a central solid axis, as is also indicated 

 in /. cervicornis. 



Formatio7i and Locality. — These specimens were obtained in the 

 shaly dolomites, below the "chert-beds" of the Niagara formation, 

 at the "Jolly-cut," Hamilton, Ont. 



Genus THAMNOGRAPTUS (Hall). 



Gr. tkamnus, a shrub; grapho, I write. 



(Palaeontology of New York, vol. iii,, 1S59.) 



"Bodies consisting of straight or flexuous stipes (simple or con- 

 joined at base ?j, with alternating and widely diverging branches ; 

 branches long, simple, or ramose, in the same manner as the stipe. 

 Substance fibrous or striate ; the main stipe and branches marked 

 by a longitudinal central depressed line, indicating the axis. Cel- 

 lules or serratures unknown." 



In this genus I have placed two species — one described in 1878 ; 

 the other, which is subject to variations — in the present paper. 

 Probably, however, there are more species of this genus in the 

 Niagara formation at Hamilton, Ontario. 



THAMNOGRAPTUS B.\RTONENSIS (SpCncer). 



Plati 6. Figs. 4 & 5. 



Thamnograptxs bartonensis (Spencer), Can. Nat., vol. viii.. No. S, :87s. 



Stipe single and broad, with lineal undulating branches, and 

 having half the thickness of the stipe. The bases of the branches 

 are nearly at right angles with the stipe, but afterward bend up- 

 ward ; these are from one to two centimeters apart, and there is 

 usually a depression of considerable length on the side opposite 

 to their place of attachment, and an expansion on the same side. 

 The texture is corneous and black, and the surface nearly smooth, 

 but with a strong medial depression half a millemetre wide (mark- 

 ing a central axis?) extends through the stipe, which is one and a 

 half millimetres broad. 



