68 



BULLETIN 65, UNITED STATES NATIONAL MUSEUM. 



Spencers diagnosis reads: 



Frond strong, with spreading braucbes, tlio margin having a plumulose ap- 

 pearance; structure corneous, with a central axis, and the surface covered with 

 minute points representing tlie cell-apertures. 



This frond somewhat resembles /. ijIuiiiuIusus, but it is slighter, and the branches 

 (not exceeding 1.5 mm. in thickness) are much more numerous and proceed from 

 a single stipe. The type specimen has a height of S and a breadth of G cm. 



Formation and localitii. — This species occurs in the Niagara limestones at 

 Hamilton, Ontario. 



Doctor Gurley describes the species as follows : 



Polypary of general dendroid aspect; main branches mostly 1-1.5 mm. thick, 

 a width of 2 mm. being only seen once, immediately below a bifurcation. 

 Branching not very regular. Usually at the proximal end several branches 







t.i 



Fig. 75. — Acanthograptus walkeri (Spbncer). 

 Copy of Spencer's figure. 



76 



Jfi^ 



77 



Figs. 7G, 77. — Acan- 

 thogeaptus wal- 

 KERI (Spencer). 



Two FRAGMENTARY 

 SPECIMENS. 



are somewhat clustered, and diverge thence radiatingly. On one specimen, 

 which I hardly feel al)le to separate, the branching is rather more from a main 

 axis. The branches, especially the main ones, are thickly beset (spinose- 

 shaggy) with the long, blunt, obliquely upward-directed denticles, which are 

 about 25 in the space of 25 mm. They differ much in appearance in different 

 parts of the polj'pary, if, Indeed, there are not more than one kind of them. 

 Sometimes on the main stem they are blunter (about 1.0 mm. long and 0.75 

 mm. wide at base), while on the branches and branchlets they are less blunt. 

 But on the main stem and principal branches longer, narrower, and less rigid 

 and regular and more hairy root-like processes occur. 



