GRAPTOLITES—GRAPTOLITOIDEA. 



33 



hydrothecse furnished with slightly incurved hook-like projections 

 on the upper outer region ; 3 basal spines. 

 Normanskill shales (Trenton), Hudson Valley. 



27. D. sextans Hall. (Fig. Si,d t e.) 



Middle Ordovicic. 



Fig. 53. a, Dicellograptus complanatus \ b, same, enlarged ; c, D. divaricatus (en- 

 larged) ; (/, D. sextans ; e, same enlarged. 



Similar to preceding, but basal spines turned up and outward. 

 Normanskill shales (Trenton), Hudson Valley. 



XIV. Diplograptus McCoy. 



Rhabdosomes linear to leaf-like, with two rows of alternating 

 oblique hydrothecse. Virgula prolonged beyond the proximal end 

 and in perfect colonies attached with others to a floating (?) central 

 disk. Ordovicic. 



28. D. pristis Hisinger. (Fig. 54.) Upper Ordovicic. 



Large oblique, acute serrations, 

 pointed exteriorly, three basal 

 spines, the central one usually 

 longest. 



Utica slate of New York and 

 other states and Canada. Europe. 



29. D. foliaceus Murchison. 



Middle and Upper Ordovicic. 

 Hydrothecae more oblique, 

 smaller and more numerous than 

 D. pristis. 

 Normanskill shales (Trenton), Hudson Valley. Europe. 



3 



FlG. 54. Diplograptus pristis. Res- 

 toration of colony by Ruedemann. /;/, 

 pneumatophore or swimming bladder ; 

 g, gonangia (N. Y. St. Geol. Rept. ). 



