Maryland Geological Survey 261 



layers 3 to 5 mm. in thickness, into small, irregular, sometimes knotty- 

 masses. Surface rough, apparently without well-distinguished maculse. 

 Zocecial apertures nearly or quite direct, irregular, more often ovate than 

 of any other shape, the lunarial side commonly the most narrowly curved 

 part of the outline; 4 to 5 in the space of 3 mm. Mesopores very variable 

 in size and distribution, averaging about two to each zooecium and usually 

 less tlian half the diameter of the latter, though sometimes exceeding that 

 dimension. Lunarium crescentic in shape when normal, but usually ap- 

 pearing more like irregularly disposed knots arising from the wall. 



In vertical section the walls of the tubes are at first rather thin ; how- 

 ever, they soon increase in thickness and become very irregular with alter- 

 nating light and dark spots, and here and there evidence of a large con- 

 necting pore. The mesopores which give one more the impression of an 

 irregular cellular or spongy tissue than of tubes, originate with the thick- 

 ening of the zocecial walls. Thin diaphragms occur in the zocecial tubes, 

 usually a little more than their own diameter apart. 



In tangential sections the proximal portions of the tubes are thin walled 

 and prismatic, farther out they are irregularly ovoid with thick, almost 

 spongy, walls in which it is difficult to distinguish the hmarium. In 

 certain areas, probably representing maculae, which occur at long intervals, 

 the mesopores are more abundant than in the intervening spaces. 



This peculiar species agrees fairly well in internal structure with 

 Ceramopora imhricata, the type of the genus, excepting that it has not 

 the basal spongy tissue characterizing that fomi, and has diaphragms 

 which have not been discovered in G. imbricata. But the zooecia and meso- 

 pores have the same indefinite wall structure and large openings in the 

 walls allowing neighboring tubes to communicate Avith each other and 

 the interstitial pores, that, in connection with the peculiar basal tissue, 

 caused Ulrich ' to restrict the genus Ceramopora to the type species. Con- 

 tinued studies have caused us to think less of the basal tissue as a diag- 

 nostic character, yet the genus remains sharply distinguished from the 

 other genera of the family. 



Occurrence. — Helderberg Formation, Keyser Member. Abundant 

 near Cumberland, Pinto, Maryland ; Keyser, West Virginia. 



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



' GeoL Surv. Illinois, vol. viii, 1890, p. 493. 



