I 



GRAPTOLITOIDEA 



127 



Graptolites commonly occur in argillaceous schists, moie rarely in limestone 

 formations, of the Upper Cambrian, Ordovician and Silurian Systems. They 

 seem to have swarmed in the muddier portions of the sea, and floated either 

 attached to sea-weeds, etc., or as free-swimming colonies ; or, in rarer instances, 

 remained stationary with the sicula or a root embedded in the mud, or attached 

 to foreign bodies. They are divided into two Orders : Dendroidea Nicholson 

 {Cladophom Hopkinson), and Graptoloidea Lapworth, or Graptolites proper. The 



:^"^?- 



Fig. 195. 



a, Münograptus gregarius Lapw. Sil- 

 urian ; Dobbs, Linn, Scotland. Proxiinal 

 end showing sicula, enlarged ; b, Didy- 

 mograptus pennatulus Hall. Ordovician 

 (Quebec Group) ; Point L6vis, Canada. 

 Proximal end .showing sicula, enlarged 

 (after Lapworth). 



Fig. 193. 



A, C, Monograptus priodon 

 (Bronn). Silurian (Etage E); 

 Prague. A, Rhabdosoma, 

 natural size. B, Longitudinal 

 section, enlarged. C, Dorsal 

 aspect, enlarged. D, Mono- 

 graptus hnhemicus Barr. Same 

 locality. a, Virgula ; c, Com- 

 mon canal ; th, Thecae ; x, 

 External aperture (after 

 Barrande). 



Fig. 194. 



a, c, Climacograptus typicalis 

 Hall, Ordovician (Trenton 

 limestone) ; Cincinnati, Ohio. 

 a, Vertical section, enlarged, 

 showing central virgula ; b, 

 Individnal of the natural size ; 

 c, Cross-section, enlarged ; d, e, 

 Diplograptus palmeus Barr. 

 Silurian ; Prague. Rhabdo- 

 soma of the natural size and 

 several times enlarged (after 

 Barrande) ; /, Diplograptus 

 foliaceus Murch, Ordovician 

 (Llandeilo Group); Scotland. 

 natural size (after Lapworth). 



Fig. 196. 



Dictyonema cavernosum Wiman. Or- 

 dovician ; Gotland. Proximal end of 

 rhabdosome with adhesion disk (x), large 

 nourishing individnal (z), and sniall 

 budding individnal or gonangium (zi). 

 3/i (after Winian). 



latter are again divided into two suborders : AxonoUpa Frech, redefined by 

 Ruedemann, without axis or virgula; and Jxonophai-a Frech, limited by 

 Ruedemann, with an axis. ^ 



Order 1. DENDROIDEA Nicholson. 



Family. Dendrograptidae Roemer. 



This family, which includes all dendroid forms, is represented during the 

 older Paleozoic by the genera Deiidrograptus, Dictyonema, Desmograptus, Gallo- 



