118 



COELENTERATA CNIDARIA 



liastrites, Barr. (Fig. 207). Hydrosoma simple, spirally coiled. Common 

 canal very narrow, virgula attenuated ; hydrothecae more or less linear, and 

 separated from one another by considerable intervals. Silurian. 



Leptograptus, Lapw. Hydrosoma consisting of two long, filiform, undivided, 

 inequal primary branches, with hydrothecae developed from major extremity 

 of the common sicula. Ordovician. 



Coenograptus, Hall (Fig. 208). Two primary branches originating from the 

 centre of a triangular sicula, curving sigmoidally, and giving off simple branches 

 from the convex side at tolerably regular intervals. Ordovician. 

 *~IHdymograptus, M'Coy (Figs. 209, 212, a). Two simple, symmetrically 



FIG. 211. 



Digeanograptus 



ramosus, Hall. 

 Ordovician 

 (Hudson River) ; 

 New York (after 

 Hall). 



:\ 



FIG. 212. 



n, Did ijmnrjrn.pt ux Murchisoni, Beck sp. Ordovician 

 (Llandeilo Group); Wales, b, Dichograptu* octobrachiatu*, 

 Hall. Ordovician (Quebec Group); Point Levis, Canada 

 (after Hall). 



FIG. 213. 



a, c, Climrn:ograj)t'Ut> t>/]>i<'<tlix, 

 Hall. Ordovician (Trenton 

 limestone); Cincinnati, Ohio; 

 , Vertical section, showing 

 common axis in the centre, 

 enlarged ; b, Polypary of the 

 natural size ; c, Cross-section, 

 enlarged. <l, r, DiplogTaptus 

 palmeus, Barr. Silurian ; 

 Prague ; <1, Polypary of the 

 natural size ; e, Polypary en- 

 larged. /, Diplograptus foli- 

 uceus, Murch. Silurian (Llan- 

 deilo Group) ; Scotland. 

 Natural size. 



developed branches springing from a small axillary sicula. Hydrothecae having 

 the form of flattened rectangular prisms, in contact throughout. Ordovician. 

 ***~Telragraptus, Salter (Fig. 210). Major extremity of sicula giving rise to a 

 non - polypif erous connecting process (funide) which sends off two simple 

 branches at each end. Hydrosoma bilaterally symmetrical. Ordovician. 



, Salter (Fig. 212, I). Hydrosoma consisting of eight simple 



