128 



NORTH AMERICAN INDEX FOSSILS. 



Fig. 1 86. a, Alonticulipora arborea, peripheral part of vertical sect, and tangential 

 sect. X 9 > ^> Atactoporella typicalis var. praedpta, surface X 9 '■> c > Homotrypa subra- 

 mosa, surface X 4/^> c// X 9 ar, d c f half of vertical sect. X 9 '■> df Prasopora simulatrix, 

 tangential and vertical sections X 9 5 <?> Aspidopora elegantula^ entire head X % '■> e ' > 

 part of surface X4-K '■> A Mesotrypa quebecensis, vertical and tangential sections X 9> 

 g, Atnplexopora cingulata, tangential sections X9 an d X 2 °« (All after Ulrich.) 



38. A. typicalis Ulrich. (Fig. 186, b.) Ordovicic. 

 Thin crusts on other bryozoans, groups of larger cells at un- 

 equal intervals, sometimes on monticules ; cells very regular. 



Utica of Kentucky and Ohio. A closely related variety (var. 

 prsecipta Ulrich) occurs in the Black River of Minnesota. 



XXVIII. Homotrypa Ulrich. 

 Frondescent or ramose, the surface showing monticules or 

 maculae of larger cells; zocecia with very thin or finely crenulated 

 walls, remote diaphragms in immature and cystiphragms in mature 

 region, and apertures often oblique. Mesopores and acantho- 

 pores present, the former few and in clusters. Ord.-Sil. 



39. H. subramosa Ulrich. (Fig. 186, c.) Ordovicic. 

 Irregularly branching; monticules low and ill- defined; axial 



region tabulated. 



Black River of Minnesota. 



