151 



by throwing off nnnierons large brandies, which sometimes anastomose. 

 Surface smootli, but liaving maculae of conspiculously larger zooecia, which 

 rise slightly above the surrounding zooecia. Six niiieulae in 1 sq. cm. Acan- 

 thopores usually not visible at the surface, but sometimes in unweathered 

 specimens, they project as very minute spiues. Mesopores absent, except 

 an occasional one in the macuke. Zooecia very thin-walled at the surface 

 in well preserved material, but thick-walled just below the surface. In 

 weathered material the zooecia appear tliick-\\'alled at the surface, owing 

 to the fact that this outer thin-walled zone has been removed. Zooecia 

 very regular in size, angular or rounded by deposits of secondary scleren- 

 chyma ; six or rarely seven in 2 nun., those in the macuke one-half larger 

 than the ordinary zooecia. 



Tangential sections show the zoacia to be angular, thick-walled, and 

 usually separated by a dark conspicuous lamina; their apertures rounded. 

 Mesopores absent, but an occasional very small zooecium, having the same 

 wall-structure as the larger zooecia is present. Acanthopores small or 

 large, abundant, from 4 to 16 surrounding a zooecium. Their walls thin, 

 indistinct, and continuous with the median lamina. The central canal is 

 nsunlly minute, and not shari>ly defined. Communication pores few or 

 absent. k 



In Ihe lor.gitudinal section the zooecia are thin-walled in the axial 

 region, slightly flexuous and crossed by straight diaphragms, from one to 

 three tube-diameters apart. The zooecia curve gradually till they reach 

 the mature region, where they turn abruptly and go straight to the sur- 

 face, and emerge at right angles to the latter. Diaphragms more numer- 

 ous in the mature region, one-half tube-diameter or less apart. Some of 

 the diaphragms are irregular, curved like cystiphragms, infundibular, and 

 either concave or convex upward. Zooecial walls abruptly thickened in 

 the mature region, except in young zoaria, and becoming very thin again 

 at the surface. Diaphragms thickened in the mature region by a secon- 

 dary deposit. 



Balostoma rarhihUc occurs abundantly in the lower 40 feet of th^ 



Whitewater division at Weisburg and Ballstown, Indiana. 

 < 



Batostoma prosseri nov. 

 (Plate V, figs. 1-lc ; Plate VI, figs. 1-ld ; Plate VII, figs. 2-2c. 

 Zoarium ramose or digitate, cylindrical, or eomjiressed, dividing dichot- 

 omously or unequally at intervals of 10 to 20 nun. ; 3 to 15 mm. in di- 

 ameter and 20 to (iO mm. long. Surface smooth, but having maculae of 



