284 Systematic Paleontology 



This is the only species of Polypora so far discovered in the Helder- 

 berg rocks of Maryland, and therefore need not be compared with other 

 forms. Several Helderberg species from other states seem to be related, 

 but none of these appear to have the same measurements. 



Occurrence. — Heluekberg Formation, Keyser Member. Cumber- 

 land. Common. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



Polypora coMrACTA (Hall) 

 Plate LI, Figs. 9-11 



Fenestella compacta Hall, 1883, Kept. State Geol. N. Y. for 1882, pi. xviii, figs. 



1-3. 

 Fenestella (Polypora) compacta Hall and Simpson, 1887, Pal. N. Y., vol. vi, 



p. 63, pi. xvili, figs. 1-3; pi. xxii, figs. 4, 5. 

 Fenestella (Hemitrypa) Nervia Hall, 1883 (in part), Rept. State Geol. N. Y. 



for 1882, pi. xxii, figs. 1-3. 



Desaiption. — " Bryozoum infundibuliform, compact. Branches on the 

 non-celluliferous side moderately strong, rounded, marked by obscure, 

 granulose striations. Bifurcations occurring at intervals of from 3 to 7 

 mm. ; width of the interstices usually less than the narrower portion of 

 the branches. Dissepiments strong, rounded, on a plane with the branches, 

 seven or eight in the space of 5 mm. Fenestrules oval, width from one- 

 half to three-fourths the length. On the celluliferous face the branches 

 are rounded, and the dissepiments angular, while the fenestrules appear 

 much narrower than on the opposite face, the branches being, sometimes, 

 nearly in contact. Cell apertures minute, circular, in two and three 

 ranges, opening directly outward, from fifteen to seventeen in the space of 

 5 mm., separated by less than the diameter of an aperture : margins dis- 

 tinctly elevated, those of the lateral ranges indenting the borders of the 

 fenestrules. 



"Width of branches .33 mm., increasing to .6G mm.; width of dissepi- 

 ments from .25 mm. to .33 mm.; length of fenestrules from .25 mm. to 

 .33 mm.'' Hall and Simpson, 1887. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Corriganville. 



Collection. — Maryland Geological Survey. 



