BRYOZOA—TREPOSTOMATA. 



137 



apertures and often few mesopores. Clusters of larger zooecia en- 

 close a stellate macula scattered over surface. 

 Stones River of Minnesota. 



71. B. (Hemiphragma) tenuimurale Ul- 



rich. (Fig. 190, /.) Ordovicic. 



Cylindrical or compressed stems with 

 thin-walled polygonal apertures, without 

 acanthopores and few mesopores ; dia- 

 phragms in peripheral region incomplete. 



Galena of Minnesota. 



72. B. (Hemiphragma) whitfieldi 



(James). Ordovicic. 



Like preceding, but more robust, and 

 with crinkled walls, readily seen on 

 broken surface 



Utica horizon of the region about Cin- 

 cinnati. 



XLIV. Stromatotrypa Ulrich. 



Encrusting, with short zocecia, oval in 

 cross section and with few diaphragms. 



Walls thin, with periodically con- 

 stricted tubuli, one or more to each 

 zocecium. Oval apertures with minutely 

 papillose peristomes, separated by de- 

 pressed interspaces. Closely tabulate 

 mesopores, rarely showing on surface. 

 Ordovicic. 



73. S. ovata Ulrich. (Fig. 188, m, 

 190, m'.) Ordovicic. 

 Encrusting shells or other Bryozoa, 



rarely free ; without monticules, but with 

 smooth areas of more widely separated 

 apertures. 



Stones River and Black River of Min- 

 nesota and Wisconsin. 



Monotrypa Nicholson. 

 Massy hemispheric or discoidal, zocecia comparatively large 

 prismatic, with thin and often crinkled walls throughout; dia- 



FlG. 191. Monotrypa tabu- 

 late,, a, fragment, X 1 5 ^> 

 tangential section, X° > c > en- 

 largement of a group of tubes 

 showing corrugations. (After 

 Hall.) 



XLV. 



