NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
435 
to be quite variable. The proliferation of the tubules obstructs even the apertura 
(fig. 7) which is nevertheless visible in the interior (fig. 8) as in Myriozoum. 
Affinities. — This species differs from Enoplostomella crassimuralis , in its large 
zooecial dimensions, its external irregularity and its many layered zoarium which 
is never vincularoid. 
Occurrence. — Vicksburgian (Byram marl) : Byram. Mississippi (common) ; 
one-half mile west of Woodwards, Wayne County, Mississippi (very rare). 
Cotypes. — Cat. No. 64290, U.S.N.M. 
ENOPLOSTOMELLA CRASSIMURALIS, new species. 
Plate 91, figs. 1-11. 
Description. — The zoarium is unilamellar, 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 olocvst 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 (ha— 0.12 mm. Peristomice \hpe=0. c Z0 mm. 
(interior) !Za=0.16mm. (exterior) \lpe= 0.20 mm. 
„ . fZs=0.70-0.75 mm. 
Z( 000 Cl cl ] 7 ~ or . * r 
Us =0.32-0.45 mm. 
Variations. — On account of the thickness of the Avails, 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 A^ery thin; the tubules are visible as round white 
spots by transparency. Their pores are all A ? ery small (figs. 6, 7) ; this is the 
reason that in tangential sections 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 rhomiboidalis , but it differs from it in its hollow zoarium and the 
much thicker, separating mural rim. 
