NORTH AMERICAN EARLY TERTIARY BRYOZOA. 717 



PLAGIOECIA DISCOIDEA, new species. 



Plate 155, figs. 12-17. 



Description. The zoarium is free, orbicular, with the form of true Discosparsa. 

 The tubes are distinct, cylindrical, smooth, bent upward at their extremity, ar- 

 ranged in regular quincunx; the peristome is elliptical, horizontal, thin. The zone 

 of growth is hardly visible. 



Diameter of the peristome 0.12 mm. 



.]/. iixurc/iii lifx. 



Distance between the peristomes 0.30 mm. 



Separation of the peristomes 0.32 mm. 



Zoarial diameters -LOO mm. 



We have not found an ovicell well enough preserved to figure. 

 Affinities. This species differs from the free forms of Plagloecia concreta in 

 its zooecia regularly arranged in quincunx on the zoarial margins. 



Occurrence. Vicksburgian (Marianna limestone) : One mile north of Mon- 

 roeville, Alabama (common). 



(. 'ot i/pcs. Cat. No. 65461, U.S.N.M. 



KEY TO DETERMINATION* OF PLAcauKC'IA AND BERENICEA. 



Most of the species of Berenicea and Diastopora which we have examined probably belong, 

 according to their exterior resemblances, to Plagioecia. We have therefore thought it necssary 

 to combine them in the same key for determination. This will facilitate the identification of 

 specimens coming from localities which have been studied. It is evident that such keys are 

 purely artificial and that they can not serve as a basis for a natural classification. Moreover 

 they are necessarily only approximations. 



IZoarium bilamellar 2. 



jjZoarium uuilamellar 4. 



IZoarium incrusting 8. 



IZoarium composite 16. 



9 fZoarium in thick, regular fronds I'lagioecia siibramosa. 



"IZoarium in thin lamellae 3. 



[Tubes margiuate Plagioecin in<ir</hiut<i. 



3] Tubes with large overlapping wrinkles-- Plagioecia lobata. 



[Tubes with thin widely spaced wrinkles.-. .-.Diastopora striatisemota. 

 4/ Zoarium discoidal (Discosparsa) 5. 



IZoarium not discoidal (Diastopora) 6. 



5/ Tubes in quincunx on the borders I'lagioecia discoidca. 



[Tubes in radial rows on the borders Plagioecia concreta. 



6<Tubes margiuate ._ .Plugivccin marginutn. 



'Tubes not niarginate 7. 



( Peristome of 0.20-0.24 mm Diastopora mugniiiuru. 

 Peristome of 0.14-0.10 mm., zooecia indistinct ._ Plagloecia tubifn-. 

 Peristome of 0.14 mm., tubes distinct Plagioecia tuboedcs. 



] Peristome of 0.12 mm., zoarium tubular ._ Diastopora tubifonnix. 



Peristome of 0.12 mm., zoarium lamellar Plagioecia laiitcllosa. 



[Peristome of 0.10 mm : _ Diastopora striatisemota. 



SfThe tubes are decorated with large overlapping wrinkles ._ Berenicea undata. 



\The tubes are smooth or striated 



qfThe tubes are very close together nearly adjacent _.30. 



\The tubes are widely spaced 11. 



f Din meter of the peristome=0.14 mm Berenicea stipata. 



10 \ Diameter of the peristome=0.10 mm__ Berenicea Itrerissiinn. 



