IJFK 



385 



Fig- 343- ORDOVTCIAN GRAPTOUTES: a, Dichograplus oclobrachialus (Hall); 

 b. Rrlfograptiis cutluiris Hall; c, Phyllograpliis ilicifoliiis Hall; d, Diplograptus pristis 

 (Hall) (restored by Ruedemann); e, TetragraptiisfriilicosHS (Hall);/, CttmacograpttU 

 bicornis (Hall); g, Didymograp&US nitidus Hall; h, Tclragniptus blgsbyi (Hall); 

 /, Pkyttograptus typiis Hall;/, Holograptns richardsoni (Hall). 



Most of them belonged to the simpler horn-shaped type (Fig. 344, 

 a), but compound and colonial 

 corals were present. The most 

 important development of the 

 nrk'nterates was the rise of the 

 gniptolites (Fig. 343), whose im- 

 portant function in correlation 

 has been referred to (p. 377). 



Some sponges (Fig. 345) at- 

 taiiu'd notable size. The record 

 of annelids (worms) is more 

 im-a.^er than in the Cambrian, 

 perhaps because the calcareous 

 sea-bottom of the Ordovician was 

 less congenial to them than the 



d 



Fig. 344. ORDOVICIAN CORALS: 

 a, Streptclasma corniculnm Hall; 6, 

 Coliinnniria alvfoltita Goldf. Both 

 simple an<l compound corals lived, 

 but they did not form great reefs as 

 in later periods. 



