PENNSYLVANIAN FOSSILS 109 



Bascomell a should be looked for on internal molds of brachiopods and 

 pelecypods or on specimens that show the interior. This bryozoan actually bored 

 into the shells of bivalves and it is preserved as a network of branches with 

 sac-like appendages. It is unlike any of the other common Pennsylvanian 

 bryozoans and the figure will identify it from all others. B. gigante a (fig. 290a) Fig.290a 

 is common in parts of the Pottsville of Ohio in which it was originally discovered. 



The more normal leaf -like bryozoans - as compared with Bascomell a - appear as a 

 regular network of rods and shorter connecting cross-bars. In Septopora the 

 cross-bars are curved or angulated; they are straight in the other genera. 

 Septopora biserialis (fig. 291) is common in some beds. 



Fenestrellin a (fig. 292) has straight rods and cross-bars 

 forming rectangular, window-like openings which have given the genus its name. 

 The cells are generally arranged in one or two rows and are not bordered by 

 ridges. Several species are common. 



Fig. 292 



Polypora is similar to Fenestrellina but the Pennsylvanian species may 

 be distinguished by the wavy ridges which separate the rows of cells, by the greater number 

 of cell rows (4 in Polypora , 1 or 2 in Fenestrellina ), and by the thickening of the 

 cross-bars near the rods, producing oval "windows" instead of the rectangular 

 ones of Fenestrellina . Polypora f astuosa (fig. 293) is a common species. 



Fig. 293 



B RACHIOPODA . The Pennsylvanian of Ohio yields an amazing wealth and 

 variety of brachiopods, fully equal to those of the Devonian and far superior to those of the 

 Mississippian. Only the commoner forms have been included in the following key. 



Key to the Commoner Pennsylvanian Brachiopods of Ohio 

 (see p. 4 for use of keys) 



1. a) Shell smooth or with concentric markings only 2 



b) Shell with radiating or concentric markings 7 



2. a) Beak on margin of shell . . . 4 



b) Beak near center of shell 3 



3. a) Outline and concentric markings nearly round Orbiculoidea 



b) Outline and concentric markings irregular Petrocrania 



4. a) With sinus and fold Composita 



b) Without sinus and fold 5 



5. a) Beaks small, not incurved Lingula 



b) Beaks large, incurved 6 



6. a) One valve nearly flat, the other convex Crurithyris 



b) Valves almost equally convex Phricodithyris 



7. a) With sinus and fold 8 



b) Without sinus and fold 12 



8. a) Hinge line as wide as the width of the shell 9 



b) Hinge line narrower than the width of the shell 11 



