NORTH AMERICAN EARLY TERTIARY BRYOZOA. 435 



to be quite variable. The proliferation of the tubules obstructs even the aportura 

 (fig. 7) which is nevertheless visible in the interior (fig. 8) as in Myriozoitm. 



Affinities. This species differs from Enoplostomella crassimuralis, in its large 

 zooecial dimensions, its external irregularity and its many layered zoarium which 

 :s never vincularoid. 



Occurrence. Vicksburgian (By ram marl): Byram. Mississippi (common); 

 one-half mile west of Woodwards, Wayne County, Mississippi (very rare). 



Cotypes.Cat. No. 64290. U.S.N.M. 



ENOPLOSTOMELLA CRASSIMURAHS, new species. 



Plate 01. figs. 1-11. 



Description. The zoarium is urdlamellar, cylindrical, hollow; it incrusts 

 small radicles of algae. The zooecia are little distinct, elongated, separated from 

 each other by a thick, smooth projection: the frontal is thick, concave; it is formed 

 of a tremocyst with very large tubules superposed on a very thin olocyst with 

 minute pores. The apertura (in the interior) is formed of a semilunar anter and 

 of a concave poster; it is transverse and oblique; the peristomice is triangular, 

 buried; the rimule-spiramen is wide and bordered laterally by the peristomial 

 avicularium. The avicularium is adjacent to the peristomice; it is triangular pro- 

 vided with a pivot and its beak is directed toward the top. 



Measurements. Apertura |7ifl=0.12 mm. Peristomice \hpe =0.20 mm. 



(interior) i Z=0.16 mm. (exterior) tZpe=0.20 mm. 



. fZ2=0.70-0.75 mm. 

 Zooecia I , nn . ._ 



lfe=0.32-0.45 mm. 



Variations. On account of the thickness of the walls, the variations of the 

 frontal are extraordinary (figs. 2-5) ; the exterior aspect does not correspond at 

 all with the view of the interior (figs. 6. 7) which is fortunately more regular. 

 The zooecia have no special walls (figs. 8, 10) ; they are invisible in thin sections: 

 an energetic consolidation must take place on the very young zooecia; the latter 

 moreover do not bear any kind of prominent separating mural rim. The tubules 

 are seen with difficulty on the transverse sections (figs. 9, 10). 



In the interior the avicularium appears as a triangular chamber adjacent to 

 the apertura. The olocyst is very thin: the tubules are visible as round white 

 spots by transparency. Their pores are all very small (figs. 6, 7) ; this is the 

 reason that in tangential section^ the tremopores are large, round, and obscure 

 spots feebly lighted by a luminous point. 



The zoarium is formed sometimes by two superposed lamellae. Very rarely 

 it is bifurcated. 



Affinities. In the external aspect of the zoarium. this species resembles 

 Enoplostomella rhomboid nils, but it differs from it in its hollow zoarium and the 

 much thicker, separating mural rim. 



