GRAPTOLITES OF NEW YORK. L'Alt'L' 1 



681) 



for but one third of their length in mature parts of rhabdosorae. Outer 

 margins concave, apertural margins straight, normal on axis of theca ; one 

 half the width of branch ; provided ^vith long, straight spines, Avhich 

 have a direction perpendicular to the axis of 

 the branch. The dorsal wall of the branches 

 also provided with perpendicular spines, 

 which alternate with the apertural ones. 

 Position and locality. Rare in the 

 shales with D i p 1 o g r a p t u s d e n t a t u s at Mt Moreno 



Fig. 84 Didymograptus splnosus 

 sp. nov. Proximal portion of branch. Ash- 

 hill quarry at Mount Moreno. x4.5 





Fig. 85 Didj'mograptus spin- 

 osus sp. nov. Portion of distal part 

 of branch. Ashhill quarry at Mount 

 Moreno, xl 



Remarks. This species is at once distin- 

 guished from all other forms of Didymograptus 

 known to me, by its double row of spines. There 

 has however been described a sjDecies of Tetra- 

 graptus (T . acanthouotus Gurley, 1896. 

 p.65), from the Beekmantown shales at Point 

 Levis, which exhibits the same spinous dorsal margin as the species in hand, 

 and which may indicate the line of descent of this Didymograptus [p.558]. 



Didymograptus bifidus Hall sp. 



Plate 15, figures 1-3 



Graptolithus bifidus Hall. Canadian Organic Remains, decade 2. 1865. p.73, 



pl.l, fig.16-18; pl.3, fig.O, 10 

 Didymograptus bifidus Nicholson. Quar. Jour. Geol. Soc. 1868. 24:136 

 Didymograptus bifidus Nicholson. Ann. and Mag. Nat. Hist. ser. 4. 1870. 



5:346, fig.7 

 Didymograptus bifidus Hopkinson & Lap worth. Quar. Jour. Geol. Soc. 1875. 



31:646, pl.33, fig.8a-e 

 Didymograptus bifidus (?) Brogger. Die sil. Etagen 2 and 3, etc. 1882. p.41 

 D idym ograp tus bifi dus Herrmann. Geo). Mag. ser. 3. 1886. 3:15 

 Didy mogra pt us b i f i d u s Ami. Geo). Sur. Can. Rep't, ser. 2. 1889. v.3, pt2, 



p.ll6k 

 Didymograptus bifidus Barrois. Ann. de laSoc. Geol. du Nord. 1892. 20:92 

 Didymograptus bifidus Gurley. Jour. Geol. 1896. 4:295 



