NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
559 
formed of thin, prominent interareolar costules, and of a false area due to incom- 
plete pleurocystal calcification. The peristomie is of little depth; the peristome 
is thin, prominent, developed distally only; the aperture (as seen from the interior) 
is semilunar with an almost straight proximal border. The avicularium is median, 
simple, triangular; its point projecting, like a spur. 
M easurements . — Peristomice 
^y)=0.10mm. 1 
7g=0.10mm. 
Zooecia 
\Lz= 0.50—0.60 mm. 
\lz= 0.25-0.30 mm. 
Observation— Photography does not give exactly the aspect of this species; 
it does not show sufficiently the very great projection of the avicularium above the 
plane of the figure. 
Bracebmdgia aculeata differs from the other known species by its straight and 
median avicularium, which is never oblique, or sublateral. 
In the interior the avicularium is invisible, and it is therefore of exterior or 
pleurocystal origin. 
Occurrence.- — Middle Jacksonian : Three and one-fourth miles south of Perry, 
Georgia (common). 
Cotypes. — Cat. No. 64188, U.S.N.M. 
BRACEBRIDGIA POLYMORPHA Rcuss, 1864, var. COSTULATA, new variety. 
Plate 71, figs. 13-23. 
1864. Eschara polymorpha Reuss, Fauna deutschen Oberoligoean, Sitzungberichte der k. 
Akademie der Wissenscbaften, Wien, vol. 50, p. 651, pi. 12, fig. 6. 
1868. Eschara polymorpha Reuss, Bryozoa deutschen Septarienthones, Sitzungberichte der 
k. Akademie der Wissenscbaften, Wien, vol. 52, p. 61, pi. 8, figs. 8-10. 
1867. Eschara polymorpha Reuss, Fauna Steinsalzablagerung, Sitzungberichte der k. Akade- 
mie der Wissenscbaften, Wien, vol. 55, p. 144. 
Measurements . — Aperture' 
A<2=0.08 mm. 
la= 0.10 mm. 
Variations. — The areolae form a line of small pores around each zooecium (figs. 
15, 20). Between them short costules often develop (figs. 17, 20). 
The pleurocyst is not very regular; it forms a prominent collar around each 
zooecium, in the form of an interrogation point. Below the avicularium there is 
an irregular, triangular area, the depth and size of which depends upon the pleu- 
rocystal activity, which is always very irregular. 
The avicularium, when it is well preserved, deforms the external aperture 
(figs. 15, 18, 21) ; it is oblique (figs. 15, 18) or transversal (fig. 17) ; the two posi- 
tions may be observed on the same zoarial fragment (fig. 21). 
The gonoecia (figs. 14, 22) are larger than the usual zooecia. 
All these characters are lessened by fossilization (fig. 23) and the zooecia 
appear very polymorphic. 
1 In the Adeonidae we give the dimensions of the peristomice or external aperture when this is somewhat 
constant, in preference to the dimensions of the apertura which can he measured only in the interior of 
the zooecia. 
