CLASS II 



H YDEOZO A— GRAPTOLITOIDE A 



129 



Order 2. GRAPTOLOIDEA Lapworth. 



Suborder A. AXONOLIPA Freeh (emend. Eueclemann). 



Family 1. Dichograptidae Lapworth. 



Uniserial Graptolitoidea tvith bilateral rhabdosome ; branches dichotorhous ; thecae 

 simple, sub-cylindrical. 



Dicliograptus Salter (Fig. 198). Ehabdosome consisting of eight simple 



Via. mo. 



Tetragraptus hryonoides Hall. 

 Ordovician ; Point Levi.s, Canada 

 (after Hall). 



Pig. 200 



Didymograptus pennatulus Hall. 

 Ordovician ; Point Levis, Canada 

 (after Hall). 



fi m 



Fig. 19S. 



Dichograptus octohrachiatus Hall. Ordovician (Quebec 

 Group) ; Point Levis, Canada (after Hall). 



Fig. 201. 



Didymograp- 

 tus murchisoni 

 (Beck). Middle 

 Ordovician 

 (L 1 a n d e i 1 o 

 Group) ; Wales. 



Fig. 202. 



Phyllograptus fypus Hall. 

 Ordovician (Quebec Group) ; 

 Point Levi.s, Canada, a, Several 

 polyparies of the natural size ; 

 h, Ideal cross-section, enlarged 

 (after Hall). 



uniserial branches which are produced by rejDeated dichotomy, and their bases 

 often enveloped in a central corneous disk. Ordovician. 



Tetragraptus Salter (Fig. 199). Rhabdosome consisting of four uniserial 

 branches which are produced by twice repeated dichotomous division. 

 Ordovician. 



Didymograptus M'Coy (Figs. 195, b; 200; 201). Rhabdosome consisting of 

 two symmetrical branches diverging from a small jDrimary cell (sicula) at 

 various angles. Thecae obliquely directed, having the form of flattened 

 rectangular prisms, and in contact with one another throughout. Ordovician. 



Phyllograptus Hall (Fig. 202). Rhabdosome leaf-like, composed of four 



VOL. I K 



