30 



BULLETIN" 77, UNITED STATES NATIONAL MUSEUM. 



limited fauna, mainly because it seems ill-suited for bryozoan life. 

 The few species occurring in it are listed below with those of the 

 Phylloporina bed. The entire bryozoan fauna amounts to 50 species, 

 with 16 occurrino: also in the Baltic area. 



BEYOZOA OF THE PHYLLOPORINA AND FUCOID BEDS. 



* Vinella repens Ulrich. 

 *Stomatopora arachnoidea (Hall). 

 *Corynotrypa delicatula (James). 

 *Corynotrypa inflata (Hall). 

 Pi'oboscina tumulosa Ulricli. 

 * Ceramo'porella granulosa minor Bassler. 

 Crepipora subsequata Ulricli. 

 Favositella laxata Ulricli. 

 Ceramoporella inclusa Ulrich. 

 Cosloclema trentonense Ulrich. 

 Ceraviophylla frondosa Ulrich. 

 *Rhinidictya mutabilis Ulrich. 

 Rhinidictya mutabilis major Ulrich. 

 Rhinidictya paupera Ulrich. 

 Rhinidictya exigua Ulrich. 

 Eurydictya multipora (? Hall). 

 Pachydictya occidentalis Ulrich. 

 Trigonodictya conciliatrix Ulrich. 

 Arthropora bifurcata Ulrich. 

 Stictoporella rigida Ulrich. 

 Stictoporella dumosa Ulrich. 

 *Ar thro stylus conjunctus Ulrich. 

 Arthrodema pulchellum Billings. 

 Chasmatopora halli (Ulrich). 

 Chasmatopora corticosa (Ulrich). 



Atactoporella ramosa Ulrich. 

 *Homotrypella cribrosa Bassler. 

 *Homotrypella hospitalis crassa (Ulrich). 

 Homotrypa minnesotensis Ulrich. 

 *Homotrypa subramosa Ulrich. 

 Ilomotrypa tuberculata Ulrich. 

 Prasopora simulatrix Ulrich. 

 Prasopora contigua Ulrich. 

 Prasopora conoidea Ulrich. 

 Prasopora lenticularis Ulrich. 

 Bythopora alcicornis Ulrich. 

 *Eridotrypa sedilis (Eichwald). 

 *Eridotrypa asdilis minor (Ulrich). 

 Dekayella prsenuntia echinata Ulrich. 

 Dekayella trentonensis (Ulrich). 

 *Hallopora muUitabulata (Ulrich). 

 Hallopora ampla (Ulrich). 

 '^Hallopora dumalis (Ulrich). 

 Hallopora pulchella (Ulrich). 

 Hallojwra pulchella persimilis (Ulrich). 

 Calloporina crenulata (Ulrich). 

 Batostoma montuosum Ulrich. 

 *Hemiphragma irrasum Ulrich. 

 Stellipora antheloidea Hall. 

 *Stigmatella claviformis (Ulrich). 



The Fucoid bed closes the Black Kiver in Minnesota, but in north- 

 ern Iowa a shaly gray limestone filled with a variety of Prasojmra iiv- 

 sularis forms the last apparent member of the group. Numerous 

 bryozoans occur in this bed, but hsts of the species have never been 

 published. However, the fauna is essentially the same as the imder- 

 lying Black River shales with about 40 per cent of the species present 

 in the Russian deposits. 



As indicated in the correlation table on page 38, the Trenton strata 

 of the upper Mississippi Valley comprise only the lower portion of this 

 group. In Minnesota the group may be divided into four faunal 

 zones. The lowest consists of yellowish to light green shales with in- 

 terbedded thin, impure limestones. Fossils of aU classes are rather 

 numerous, although the bryozoans as usual make up the largest part 

 of the fauna. A species of Clitamhonites is one of the characteristic 

 fossils and has given the name to the bed. Thirty-six species of 

 bryozoans have been recorded from the Clitambonites bed, and of 

 these, 16 occur also in the Baltic Middle Ordovician. The similarity 



