GRAPTOLITES—GRAPTOLITOIDEA. 



29 



12. D. (Goniograptus) thureaui McCoy. (Fig. 4.1, d, 42.) Lower 

 Ordovicic. 



Four nearly rectangular main branches of a zigzag outline with 

 regularly alternating secondary branches. 



Lower graptolite shales of 

 Quebec and Hudson Valley 

 (Beek man town). Also Euro- 

 pean. 



VIII. Tetragraptus Salter. 



Typically of four short and 

 broad branches with large hy- 

 drothecae. A common trans- 

 verse stem (funicle) occurs. A 

 group still classed here is like a 

 Dichograptus with only four 

 arms, and a quadrangular cen- 

 tral disk. It really belongs to 

 a distinct genus. Ordovicic. 



13. T. bigsbyi Hall. (Fig. 43.) Lower Ordovicic. 

 Of four short broad arms, with narrow but long hydrothecae 



mucronate at the margin. Strong central stem. 

 Lowest graptolite beds (Beekmantown) of 

 Point Levis and Hudson Valley. 



14. T. quadribrachiatus (Hall). (Fig. 41, 

 b.) Lower Ordovicic. 

 Like half a Dichograptus octobracliiatus — 



long slender branches with small hydrothecae 

 and a quadrate central disk. 



Lower graptolite beds (Beekmantown) of Canada and Hudson 

 Valley. Also Europe. 



Fig. 42. Goniograptus thureaui. 



Fig. 



43. Tetragraptus 

 bigsbyi. 



IX. Phyllograptus Hall. 



Like letragraplns with the four branches grown together, each 

 two back to back, forming a cross in section — generally preserved 

 in flattened form so as to appear as a single leaf-like body. Or- 

 dovicic. 



15. P. typus Hall. (Fig. 44.) Lower Ordovicic. 



Broad, oval to lanceolate, as appearing on shale, with 24 (22-26) 



