151 



by throwing off iiuuieious larjie braiR-lies. wliirli sonu'tiiues lumsluinose. 

 Surface siuootli, but hMving uineuhie of consi>icul()usly larger zooecia, which 

 rise slightly above the surrounding zocecia. .Six maculae in 1 sq. em. Acan- 

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

 specimens, they project as very minute spines. Mesopores al)sent, except 

 an occasional one in the niai-ula'. /(xeeia very thin-walled at the surfac(j 

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

 weathered material the zocecia appear thick-walled at the surface, owin^ 

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

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

 cliyma ; six or rarely seven in l' nnu., tlmse in the macula' one-half larger 

 than the ordinary zofecia. 



Tangential sections show (he zocrcia to be angular, thick-walled, and 

 usually separated by a dark conspicnons lamin;i : their apertures I'ouniled. 

 Mesopores absent, but an occasional very small zcxecium. having the same 

 wall-structure as the larger zcMccia is ju'esent. Acanthopores small or 

 large, abundant, from 4 to lO surrounding a zcxecium. Their walls thin, 

 indistinct, and continuous \^'ith the median lamina. The central canal is 

 usually nnnute. and not sharply defined. ( "omnmnication pores few or 

 absent. ^ 



In t'jc lo'.gitudnial section the zixecia are tliin-w.-iUed in the axial 

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

 three tube-diameters apart. Tlie zorjocia 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-lialf tube-diameter or less apart. Some of 

 the diaphragms are irregular, curved like cy.stiphragms, infundibular, and 

 either concave or convex upward. Zocecial walls abruptly thickened in 

 the mature region. excei)t in young zoaria, and becoming very tliin again 

 at the surface. Idaphragms thickened in the mature region l\v a secon- 

 dary deposit. 



liatostonia niiiahUc occurs abundantly in the lower 40 feet of the 

 Whitewater division at Weislturg and I>allstown, Indiana. 



Ratostoma prosseri nov. 

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

 Zoarium ramose or digitate, cylindrical, or coini)ressed, dividing dichot- 

 omously or une(pially ;it intervals of 10 to 20 mm.; ?> to l.T mm. in di- 

 ameter and 20 to CO mm. long. Sui-f:ice smooth, but having maculae of 



