NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
93 
finely crenulated. On the dorsal olocvst there are two large distal impressions. 
The very large distal septula is double in the primoserial zooecia. There are three 
septal ae to each lateral wall. The interopesial cavities are very small, triangular, 
and rather constant. 
Measurements. — Opesia 
I ho-— 0.24-0.26 mm. 
I lo~ 0.20-0.22 mm. 
Zooecia 
|Zs= 0.32-0.36 
lfe=0.30 mm. 
mm. 
Variations. — The young zooecia are the more perfect; their mural rim is thin; 
the large distal septula and the impressions are quite visible (fig. 6). The other 
zooecia have a mural rim enlarged at the base (fig. 8). The primoserial zooecia are 
engendered, following the rule, by a zooeeium of larger dimensions (figs. 6, 8). 
The origin of the multiplicity of the lamellae is quite remarkable. On the 
zoarium may be perceived a sort of subcolonv, one superimposed upon the other, 
which does not arise from one fixed larva. When the two distal septulae are not 
on the same plane (fig. 5), the uppermost septula corresponds to another higher 
lamella of zooecia covering the normal one and the first of these zooecia is like 
an ancestrula of the subcolonv which comes forth then as a spiral. This disposition 
is clearly visible on figure 5. 
Deformed zooecia are common. They result quite often from the meeting of 
two subcolonies (figs. 3, 4). Sometimes they appear on the zoarium as zooecia 
wanting in vigor and incapable of engendering a new zooeeium (fig. 3) ; then the 
two lateral lines are rejoined above them. Their forms are very capricious and 
escape all analysis. 
The zoarial lamellae are intimately united because of their formation by sub- 
colonies. Sometimes, however, the lamellae back to back are separable (fig. 7). 
The dorsal then bears very remarkable, long, prismatic lines on which the zooecia 
are invisible. 
The lateral walls bear three large septulae. 
Affinities. — This species differs from Conopeum arborescens in its zoarial form 
and its elliptical opesium. On account of its large zoarial dimensions it is a strik- 
ing and good guide fossil, and it may be determined easily in the field. 
Occurrence. — Lower Jacksonian (Moodys marl) : Various localities about Jack- 
son, Mississippi (common) ; 24 miles north of Robert, Mississippi (common). 
Cotypes. — Cat. No. 63872, U. S. N. M. 
CONOPEUM ARBORESCENS, new species. 
Plate 20, figs. 10-16. 
Description.— The zoaria encrust algae, surrounding them with many superim- 
posed lamellae, and thus forming free, irregular, branched, hollow masses. The 
zooecia are large, separated by a ridge, elongated, elliptical, or pyriform ; the mural 
rim is fiat and very little enlarged at the base. The opesium is oval. The inter- 
opesial cavities are very small, constant, elliptical, or triangular. 
Measurements . — Opesia 
\ho = 0.30-0.32 
|7o=0.18 mm. 
mm. 
Zooecia 
\L 
(fe 
3 = 0.46-0.50 
=0.30 mm. 
mm. 
