216 SYSTEMATIC PALEONTOLOGY 



clusters of large zooecia. Generally, at the center of each of these clusters, 

 the mesopores which are small and in nearly all cases just about numerous 

 enough to isolate the zooecia, are gathered into groups of varying size. 

 Zocecial apertures circular, those in the clusters attaining a diameter of 

 0.4 mm., while those of the smaller size in the inter-macular spaces 

 average about 0.22 mm., with 11 or 12 in 3 mm. 



"Internal Characters: The first peculiarity to be noticed in tan- 

 gential sections is the relatively great abundance of the mesopores. In 

 most specimens they form a complete ring around the zocecia, and it is 

 chiefly the large cells in the clusters that are occasionally in contact at 

 limited points. The zocecial walls are thin. The cystiphragms are more 

 numerous and extend to a less distance from the walls than in any other 

 American species. The opening left by them is of various shapes, gen- 

 erally subangular, and often removed from the walls. True acanthopores 

 have not been detected. 



" In vertical sections the abundance of the mesopores, the narrowness 

 of the cystiphragms, and the unusual crowding of the tabulation in both 

 sets of tubes, are the distinctive features. In the mesopores the average 

 number of diaphragms in 1 mm. is over 25, while the cystiphrams may 

 number as high as 20 in 1 mm., though the average is not likely to be 

 over 15 in that space." Ulrich, 1893. 



Occurrence. CHAMBERSBURG LIMESTONE (Echinospherites bed). 

 Pinesburg Station, Maryland. This species has hitherto been known 

 only from the lower Trenton (Prosser limestone) of Minnesota. 



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



PRASOPORA CONTIGUA Ulrich 

 Plate XLVII, Figs. 7, 8 



Prasopora contigua Ulrich, 1886, Fourteenth Ann. Kept. Geol. Nat. Hist. 



Surv. Minnesota, p. 87. 

 Prasopora contigua Ulrich, 1893, Geol. Minnesota, vol. iii, p. 249, pi. xvi, 



figs. 24-26. 



Description. " Zoarium hemispheric, base flat or slightly concave, 

 usually less than 30 mm. in diameter. Zocecia with very thin walls and 



