NORTH AMERICAN EARLY TERTIARY BRYOZOA. 



493 



It di tiers from Porellu jncL'xonicn in its zoarial fronds ;.ot spread out and 

 very narrow, in its much wider uml><> and in its still larger tremopores. 



<><-<_-]irrcn<-c. Vieksburyiaii (Hyraui marl): Byram, Mississippi (very rare); 

 one-fourth mile west of Woodward, Wayne County. Mississippi (common). 

 .Cat. No. 64303. T.S.X.M. 



Geological ilixtrilniiinn of American species of Pordln. 



ANALYTICAL KEY TO AMElilCAX SPECIES OF PORBLLA. 



Zoariuui vincuhii 1 



Zoariuin incriisting 



Zonriuiu eseharian 



Zc'iarium inii lamellar 



fAviciilarium median, trianjrul:ir_- 

 2JAvicularium quite salient on nmbo_- 

 I Avicularium little salient__ 



Porclla ci/Uiiilrifit. 

 9 



JAvicularium adventitious on the peristome__ 

 [ Avicularium not adventitious on the peristome_ 



[Frontal granular 



|Xo granules, zooeeia irregular-- 

 [Aviciihirimn median, very s;ilient on uml>i>_- 

 | Aviriilarinm small, not salient _. 



, ft'iiiho nearly straight 



|Avicnlarian nmbo oblique__ 



10 

 .Porella 



.Porrllti limit/ens. 



-Porella coronatn. 



.4 



.Porella {irnntilosa. 



-Pordln irri'iniliirix. 



fAvicnlariaii limbo Inrge and short- 

 7{AvirnIaria 



MAvicniarian uinbo thin, denticulate, very large tremopores- 

 [Avicularian umbo thin, tremnpi>res-- 



-Poreltii ci'iftii. 

 _7 



I'nri'llil rniHiiitrttl. 



I'ni-i lln ih ntii-iiUfrrii. 



10 



Large zooeeia CL?=1.10 mm.L avieularia invisibUv. . 

 | Siiiallc-r y.niici-ia . 

 fFronlal \viih separated tremopon s 



Frontal with adjacent tremopoivs : avicnlaria -hardly visible 



Large a\ iciilarian umbo very salient-- 



Avicularium not salient, small. 



I'nfi'lln /inr/i'iilosa. 



I'm-i'llii uli/litii. 



I'm-* tin unguiculata. 



-Pordln crassoparies. 



