530 



GEOLOGY 



Cambrian brachiopods (Figs. 390 and 373) will illustrate, in some 

 degree, their changes. 



The Bryozoans. The bryozoans (Fig. 391), kin to the brachio* 

 pods (p. 945) were very unlike them in external form, in habits, 



Fig. 392. Ordovician Echinoderms: a, Comaroci/stis punctatus Billings; 

 b, Lepidodiscus cincinnatiensis (Roemer); c, Pleurocystis filitextus Hill- 

 ings; d, Ectenocrinus grandis (Hall); e, Dendrocrinus polydoetylut 

 (Snumard); /, Hybocrinus tumid us Billings; g, Lepadocuxtis moorei 

 (Meek); h, Carabocrinus vancortlandti Billings; i, Archofocrimu <l<-xid- 

 eratus Billings; /, Glyptocrinus decadacti/lus Hall; k, Anomalocrinns 

 incurvus M. and W.; I, Palceaster simplex Miller, a, b and care cyst oi< Is, 

 d-k are crinoids, I is a star-fish. Cystoids and crinoids were the most 

 numerous echinoderms of the Ordovician. 



and in their hard secretions. The bryozoans lived in colonies, con- 

 nected by a common mantle which secreted calcareous material to 

 form the framework of the colony. These secretions so closely re- 



