GRAPTOLITES OF NEW YORK, PART 2 1 89 



is exposed to weathering, the fossil soon disappears, so that it is only on 

 freshly fractured surfaces that the structure is preserved. 



It is cited as occurring in the "Niagara shale at Lockport, Rochester 

 and other places." 



Spencer has recorded the form from the Niagaran limestone at Ham- 

 ilton, Ontario. 



Gurley, in his manuscript, adds to the descriptions of Hall and Spencer 



the following note : 



Two specimens from the Niagara formation, at Hamilton, Ontario, are 

 figured [see fig. 134, 135], showing the blunt toothlike bodies and the 

 apparently dentate margin. While the appearance much resembles thecae, 

 it is impossible to make a positive statement on the material available. 



From a fairly large series of good specimens we derive the following 

 data on this important species : 



The rhabdosome is arborescent in form ; the branches divide dichoto- 

 mously at irregular intervals, forming initial angles of 5o°-6o° but becoming 

 later subparallel ; of large dimensions (maximal length of largest fragment 

 observed 14 cm, width of another 17 cm), the stem near base 5 mm thick, 

 the branches quite uniformly 3 mm. The branches diminish hardly toward 

 the distal extremities which are bluntly rounded. The stem is apparently 

 smooth, the branches are thickly set with short tubular processes which 

 project about 1 mm from the body of the branch, are of uniform width, 

 directed upward and clistally slightly bent backward and number, counted 

 along the margin, about 14 in 10 mm. On specimens where the body of 

 the branch has weathered away, exposing the apertures of the reverse side, 

 they are seen to be distributed about equally over the whole branch, being 

 approximately arranged in quincunx and numbering about five in the width 

 of the stem. At the extremities of the branches they form dense tufts. 



Remarks. The general habitus of I. plumulosa can be best 

 described by a comparison with a Lepidodendron or a Lycopodium ; it not 

 only resembles these plants in the mode of its branching and the uniformly 

 wide, blunt ending branches but also in their scaly appearance. 



Hall's original and later improved figures give a good conception of 

 the general appearance of the form. A more complete specimen from the 



