Fit;. 341. ORDOVICIAN BRYOZOANS: a, Conslcllar'ui polystomcUa Whitfield; b, 

 Crcpif>ora ht-niisphfrica Ulrich; c, Stromatopora ddicatnto (James); d, a part of c, 

 d; e, Callopora putchclla Ulrich, /, a part of e enlarged; g, Rhinidictya mu- 

 '>ilis Ulrich, h, a part of g enlarged. 



:retions. They lived in colonies, which secreted calcareous mate- 

 il. These secretions resemble coral so closely that they have 

 jen mistaken for it. In the middle and later portions of the 

 ;riod, the secretions of bryozoa contributed much of the limestone. 

 Echinoderms (p. 686), represented now by such forms as star- 

 sh and sea-urchins, were plentiful. The cystoids reached their 

 limax before the close of the period; the crinoids became prominent, 



