NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
161 
Measurements — Opesia \^° mm ' 
Avicularia 
7e>=0.16 mm. 
Lav= 0.35 mm. 
\Jav= 0.20-0.25 mm. 
Zooecia 
|Zs=0.40-0.45 
\lz= 0.35 mm. 
mm. 
Affinities . — The presence of the gymnocyst modifies the zooecial length very 
much, and it is not rare to observe zooecia 0.60 mm. in length. The difference 
between this form and A. flammeum is small ; the mural rim is not complete and 
the larger avicularium is terminated only by a beak having a small narrow canal. 
Many zooecia have no cryptocyst and these have considerable resemblance to 
Callopora tenuirostris Hincks. 1880, but this variety is not common enough to cause 
errors in identification. Figure 3 on plate 30 is of a specimen altered chemically. 
Figure 2 is perhaps of this species representing the region of the ancestrula. 
Occurrence. — Upper Jacksonian (Ocala limestone) : Old Factory, 14 miles 
above Bainbridge, Georgia (very rare) ; 4 miles below Bainbridge, Georgia (very 
rare) ; 7 miles above Bainbridge, Georgia (very rare) ; Bainbridge, Georgia (very 
rare). 
Cotypes. — Cat. No. 63931, U.S.N.M. 
AMPHIBLESTRUM ORBICI) LATUM, new species. 
Plate 30, fig. 4. 
Description. — The zoarium incrusts shells. The zooecia are distinct, little 
elongated, suborbicular, separated by a deep furrow; they are surrounded by a 
small gymnocyst; the mural rim is thin and salient; the cryptocyst is flat, orbicular, 
perforated with very scattered tremopores. The opesium is semilunar, surrounded 
by a salient peristome, the distal part of which bears from 4 to 6 spines. The ovicell 
is hyperstomial, globular and salient; it opens above the operculum by a special 
orifice. The small avicularia are rare, interzooecial, and triangular. There are two 
pairs of lateral dietellae. 
Measurements . — Opesia 
1^0=0.05 mm. 
|?o=0.07 mm. 
Zooecia 
Zs= 0.35-0.40 mm. 
fe=0. 32-0.35 mm. 
Affinities. — The genus Thairopora was proposed by MacGillivray in 1890 for 
the species provided with a calcified cryptocyst and with an operculum corre- 
sponding to the opesium. This is precisely the case in our American species where 
the opesium is transformed into a real aperture. But the species of Thairopora 
have some characters entirely different, such as interzooecial avicularia, internal 
spicules, and labial processes. We are therefore unable to classify this American 
species in that genus. 
In its external aspect this species resembles a Mieropora , but it differs from 
that genus in its hyperstomial, not endozooecial ovicell, and in the absence of 
opesiules. 
In the ensemble of its characters, interopesial avicularia, oral spines, hyper- 
stomial ovicell, this is surely an AmpMblestrum , of which it forms a very divergent 
55899— 19— Bull. 106 11 
