314 



BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



a concentrically wrinkled epitheca. Average specimens are several 

 centimeters in diameter, but examples as wide as 15 cm. occur. 

 Upper surface celluliferous, smooth; maculae inconspicuous, com- 

 posed of more numerous mesopores and of zooecia larger than else- 

 where. Zooecial apertures polygonal, averaging 0.50 mm. in diam- 

 eter, with three in 2 mm.; walls thin. Mesopores variable in size 

 and shape, and rather numerous. 



The shape of the zoarium and the internal characters of the Swedish 

 specimens studied by Nicholson are shown in figure 192, while thin 



Fig. 193.— Diploteypa peteopolitana. a, tangential section, X20, showing NtrMEEotrs mesopores; 



6, A portion of the same, X35, ILLUSTEATING SIMPLICITY OF WALLS; C, VEETICAL SECTION, X8, "WITH 

 USUAL ARRANGEMENT OP DIAPHRAGMS; d AND e, PORTIONS OP A VEETICAL SECTION, X20, WITH A FEW 

 CURVED DIAPHRAGMS. KEGEL BEDS (D2), KEGEL, ESTHONli.. 



sections of Russian examples are illustrated in the following figures. 

 In tangential sections the absence of acanthopores, the tenuity and 

 simple character of the walls, and the polygonal shape of both zooecia 

 and mesopores are most noticeable. The most important specific 

 character is seen in vertical sections or in vertical fractures showing 

 the tabulation. In the mesopores the diaphragms average a tube 

 diameter apart, thus, in comparison with the zooecial tubes giving a 

 crowded effect. The same average holds for the zooecia proper, 



