150 



low or very (leep t;iiijj:eiitial sections the zocecia are thinner walUnl and 

 angular, and in the deep sections the mesopores apix^ar to l)e more nu- 

 riierous. 



In lont^itiidinal sections the zocecia are s(>en to he thin-walletl and 

 without diaphra.LjMis in the axial re.i^ion, and ,i,'raduall.v curvinji; to the sur- 

 face, they emerge at riglit angles to the latter. The mature region is 

 fairly deei> and liere the zoa'cia are thick-walled, e.xcept very close to the 

 surface. Diaphragms from 2 to S in each zcxpcial tuhe. in the mature 

 region, one-half to two tulte-dianictcrs apart, the first one usually not 

 nearer than two tube-diameters tn tlic surface <if the znariuni : mi:re nvi- 

 merous in the "mesopores. which present a chain-like aiipearaiice. In the 

 suhmature region the acanthopores are thin-walle<l with a wide canal, 

 crosseil by numerous diaphi'agnis. The external jiortion of the walls of 

 the acanthopores as seen in longitudinal sections presents a spiny appear- 

 ance, due apparently to an interrupted or periodic dei>osition of scleren- 

 chyma. 



Accoi'ding to liassler. liiitostniini rdJiinis is "aliundant in llie Arnheim. 

 Waynesville. fJberty and Whitewatei- formatidus of the Richmond group 

 in Ohio, Indiana and Kentucky."' It occurs in the Tanner's Creek section 

 rarel.v in the Aiiiheim and lower sixty feet of the Waynesville. ar.d 

 abundantly in the upper thirty feet of the Waynesville and liiwer twent\ 

 feet of the Liberty foiMiiatious. It does n()t (iccur in the uiijier Lib- 

 erty. Sahnla or Wliitewalei- furmations in Indiana. The Whitewater 

 fiii'ni is IS. i-iiriiihUc. li. rdrhnis occurs in the base of the Tyi])erty near 

 .\bington, Wayne ("ounly, Indiana, and in the .\rnlicini and Waynesville 

 ne;u' Madison. 



I'.vrosTOMA \ AiiiAiiiLi; (riricli). 

 il'hilr II. lius. Me: I'lat;' III, liys. 1 Ic: I'latc I\". lius. 1. la: IMalc \'1I. lius. 1-lc.l 

 lialonlnimi rariiihilc (pars), rii-ich. (;e<)l. Surv. III.. \'ol \III. isOO. 1)1. 



xxxvi, Fig. I. ( non jil. x.xxvi, Figs. lit. \i\ li. ntriinis) . 

 lUihislniiKi niridhilc. r.assler. I'roc. T'. S. Xat. Mas., \i>]. XXX. I'.KX;. p. 



IS, III. vii. Figs, it, 10. 

 lUilnsloiiiti rdriiihilc. Cumhigs. Indiana l>ept. (ieol. Xat. Ues. ;i'Jd \uu. 



Ifei''-. 1"-i'*7, p. 777, pi. xxvi. Fig. 1."!. 

 /oai'iniii ramose, robust, cylindrical oi- subcylindrical. ." to "JO nun. in 

 diaiiiclci'. ,aiid II) lo 7o mm. long, dividing e\-er.\ 1(> to "_'(» mm. eilliei' dii-bot- 

 oninusly or irregularl.x . Tlic b.is.il exp.iiislon forms large in-CLrular masse.-; 



' I'roc. II. S. Xalioiial Miis.nin. vul, xxx. r.iOC, ]>. IS, 



