584 



GEOLOGY 



articulate brachiopods still persisted as a minor factor, while the 

 more highly differentiated forms attained wide diversity and high 

 rank. The spirifers reached the greatest extension of their hinge- 

 line (j, Fig. 419) a feature peculiarly characteristic of the Hamilton 



Fig. 419. Representative Hamilton Fossils; a, Fenestella emadata Hall, 

 a type of bryozoan common in the Middle Devonian; b, Arthm- 

 cantha punctobrachiata Williams, one of a genus of crinoids restricted 

 to the Middle and Upper Devonian; c, Eleutherocrinus cosset hi ui 

 S. and Y., a peculiar, irregular blastoid; during life it probably rested 

 upon one side on the sea bottom, d, Echinocaris punctata (Hall), a 

 crustacean more highly organized than the trilobites. e-j, brachiopods: 

 e, Tropidoleptus carinatus (Con.); / and i, Chonetes coronatus (Con.): 

 g, Vituiina puslulosa Hall; h, Rhipidomella vanuxemi Hall, a representa- 

 tive of the orthids, which had great development in the Devonian: 

 /, Spirifer pennatus (Atw.), one of the long-hinge-lined spirifers most 

 conspicuous in the Middle and Upper Devonian; k, I, and m, pelecypods: 

 k, Cypricardella bellistriatus (Con.); I, Pterinea flabella (Con.); m, /W- 

 ceoneile constricta (Con.); three pelecypods common in the Hamilton. 

 n, Loxonema hamiltonice Hall, a gastropod common in this epoch; <>. 

 Goniatites vanuxemi (Hall), a characteristic cephalopod of this I'M HUM: 

 p, Phacops rana (Greene), the most common trilobite of the Hamilton, 

 and representative of a genus which has its greatest expansion in the 

 Devonian; q, Cryphceus boothi Greene, one of the last of tne dalmanites. 

 Note the serrated margin of the tail. 



