28 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



are almost always found on the surface of thin-bedded limestone 

 layers containing more calcareous material than usual. As indicated 

 in the following table, but a single species of this fauna has been 

 noted in Russian strata. 



BRYOZOA OF THE PLATTEVILLE LIMESTONE IN MINNESOTA: 1 



Rhinidictya trentonensis Ulrich. 

 Rhinidictya nicholsoni Ulrich. 

 Rhinidictya pediculata Ulrich. 



Escharopora angularis Ulrich. 

 *Leptotrypa hexagonalis Ulrich. 



The soft green shales and thin-bedded limestones comprised in the 

 first division of the Decorah shale, the Stictoporella bed, frequently 

 contain so many bryozoans that other fossils, in comparison, seem 

 to be wanting. Several species of Stictoporella, Pachydidyafrondosa, 

 and Anolotichia impolita, are characteristic of the bed, but a majority 

 of the species pass into the succeeding beds of the Decorah shale. 

 Of the entire fauna, 38 species, 14 are present in the Baltic Middle 

 Ordovician, where most of them occur in the formations ranging 

 from B3 to D3. 



BRYOZOA OF THE STICTOPORELLA BED. 



*Corynotrypa delicatula (James). 

 Berenicea viinnesotensis Ulrich. 

 Favositella laxata Ulrich. 

 *Anolotichia impolita Ulrich. 

 Ceramoporella distincta Ulrich. 

 Ceramoporella inclusa Ulrich. 

 ^Rhinidictya mutabilis Ulrich. 

 Rhinidictya exigua Ulrich. 

 Rhinidictya fidelis Ulrich. 

 Rhinidictya trentonensis Ulrich. 

 Pachydictya foliata Ulrich. 

 Escharopora angularis Ulrich. 

 Escharopora ? limitaris Ulrich. 

 * Escharopora subrecta Ulrich. 

 *Arthropora simplex Ulrich. 

 Stictoporella angularis Ulrich. 

 "^Stictoporella cribrosa Ulrich. 

 Stictoporella angularis intermedia Uhdch. 

 Stictoporella frondifera Ulrich . 



*Arthrostylus obliquus Ulrich. 

 *IIelopora divaricata Ulrich. 

 * Chasmatopora reticulata (Hall). 

 Monticulipora grandis Ulrich. 

 Homotrypa minnesotensis Ulrich. 

 Homotrypa exilis Ulrich. 

 Homotrypa separata Ulrich. 

 Aspidopora parasitica Ulrich. 

 *Dehayella prxnuntia simplex Ulrich. 

 ^Dekayella prxnuntia nxvigera Ulrich. 

 Hallopora angularis (Ulrich). 

 Hallopora incontroversa (Ulrich). 

 *Batostoma fertile Ulrich. 

 ^Batostoma fertile circulare Ulrich. 

 Batostoraa ? decipiens Ulrich. 

 *Hemiphragma irrasum Ulrich. 

 Stomatotrypa ovata Ulrich. 

 Nicholsonella ponderosa Ulrich ?. 

 Leptotrypa informis Ulrich. 



The lithology of the next bed, named the Rhinidictya bed on 

 account of the large number of Rhinidictya mutabilis contained in 

 it, is very similar to the underlying Stictoporella bed. The simi- 

 larity is borne out by the faunas, which differ only because of the 

 new species introduced. Of the bryozoans, 58 species have been 

 described, and of these 23 are known in the Baltic strata 

 underlying Fl. 



1 In this and the following lists, all species marked (*) are common to Russia and America. 



