THE DEVONIAN PERIOD. 



471 



h 



Fig. 210. — The Hamilton Fauna.. Crustacea: a, Echinocaris punctata (Hall), one 

 of the phyllocarid crustaceans, a group more highly organized than the trilobites; 

 b, Protobalanus hamiltonensis VVhitf., a sessile cirriped; one of the earliest repre- 

 sentatives of these degenerate crustaceans. Cephalopoda: c, Goniatites vanuxemi 

 (Hall), one of the goniatites which become more numerous in this fauna. Bryozoa: 

 d, Fenestella emaciata Hall, one of the fenestelloid forms which became very 

 abundant in the Middle Devonian faunas. Pelecypoda: e, Pterinea flabella (Con.); 

 /, Palai neil) constricta (Con.), and g, Cypricardella bellisiriatus (Con.); three of 

 the common forms of pelecypods in the Hamilton fauna. Gastropoda: h, Loxonema 

 hamiltonice Hall, a high spiral shell of a form not uncommon in this fauna. Brach- 

 iopoda: i, Spirifer pennatus (Atw.), one of the long-hinge-lined spirifers more 

 conspicuous in the Middle and Upper Devonian than elsewhere; j, Rhipidomella 

 vanuxemi Hall, one of the orthid genera which has its great development in the 

 Devonian; k, Tropidoleptus carinatus (Con.); I, Vitulina pustulosa Hall, and m 

 and n, Chonetes coronatus (Con.), three peculiar species of brachiopods in the Hamil- 

 ton fauna. They have their closest relationships with South American, Middle 

 Devonian species. Echinodermata: o-p, Eleutherocrinus cassedayi S. and Y., a 

 peculiar, irregular blastoid whose form has been modified by the loss of its column 

 and its pentamerous symmetry. During life it probably rested upon one side 

 on the sea-bottom; q, Arthrr.acantha punctobrachiata Williams, a peculiar genus of 

 crinoids restricted to the Middle and Upper Devonian faunas. It is characterized 

 by the presence, on the plates of the calyx, of movable spines similar to those on 

 the sea-urchins. Trilobita: r, Phacops rana (Greene), the most common trilobite 

 of the Hamilton fauna. The genus, although present in the Silurian, has its great 

 expansion in the Devonian; s, Cryphams boothi Greene. This is one of the last 

 of the dalmanites. Note the serrated margin of the tail and compare with Figs- 

 208, k, and 203, u. 



