CLASS II 



GEAPTOLITOIDEA 



127 



Graptolites commonly occur in argillaceous schists, more 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 

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



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CtK 



Fig. 193. 



A, C, Monograptus priodon 

 (Broun). Silurian (Etage E) ; 

 Prague. A, Khabdosoma, 

 natmal size. B, Longitudinal 

 section, enlarged. (', Dorsal 

 aspect, enlarged. D, Mono- 

 graptus bohem icna Barr. Same 

 locality, a, Virguki ; c, Com- 

 mon canal ; th, Thecae ; x, 

 External aperture (after 

 Barrande). 



Fig. 194. 



n, c, Climacograptus typicalis 

 Hall. Ordovician (Trenton 

 limestone) ; Cincinnati, Ohio. 

 a. Vertical section, enlarged, 

 showing central virgula ; b, 

 Individual of the natural size ; 

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

 Diplograptus palmeut: Barr. 

 Silurian ; Prague. Khabdo- 

 soma of the natural size and 

 several times enlarged (after 

 Barrande) ; /, Dijilograptni- 

 /oUmvui! Murch. Ordovician 

 (Llandeilo Group) ; Scotland, 

 natural size (after Lapworth). 



SI 



Fig. 195. 



a, Munograpttns gregarias Lapw. Sil- 

 urian ; Dobbs, Linn, Scotland. Proxiiual 

 end showing sicula, enlarged ; /;, Dhit/- 

 inogmjitus punnatulug Hall. Ordovician 

 (Quebec Group) ; Point Levis, Canada. 

 Pro.vimal cud showing sicula, enlarged 

 (after Lapworth). 



Fig. 196. 



Dictyonema cavernosum Wiman. Or- 

 dovician ; Gotland. Proximal end of 

 rhabdosome with adhesion disk (,r), large 

 nourishing individual {z), and small 

 budding individual or gonangium (z{). 

 3/j (after Wiman). 



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

 Ruedemann, without axis or virgula; and Axonophora Freeh, limited by 

 Ruedemann, with an axis. 



Order 1. DENDROIDEA Nicholson. 



Family. Dendrograptidae Eoemer. 



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

 older Paleozoic by the genera Dendrocjmpius, Dictyonema, Desmograpius, Callo- 



