446 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
Measurements. — Apertura \ka= 0.11 mm. Peristomicef4pc=0.1 8 mm. 
(interior) |Z«=0.11mm. (interior) 7/?e=0.12mm. 
r , . ( Lz=Q. 50-0.60 mm. 
Zooecia L . __ „ . „ 
\lz= 0.30-0.40 mm. 
Variations. — The peristomice is quite variable in its general form: it is often 
provided with a rimule-spiramen (figs. 17, 18), but there are some entire fronds 
which are entirely without it (fig. 20). The ovicells are quite variable in form 
and size (figs. 17-19). The two oral avicularia are symmetrical (fig. 20), but very 
often there is only one large oval avicularium with pivot, having its beak turned 
outward (fig. 19). 
The longitudinal section (fig. 21) shows that the ovicell is almost as large as 
the zooecium itself, and that the apertura of the ovicelled zooecium is smaller than 
that of the other zooecia. 
Affinities. — The symmetry of the rimule-spiramen is very characteristic and 
permits one to easily distinguish this species. 
It differs from Metradolium grande, in which the rimule-spiramen is often 
symmetrical, in its smaller micrometric dimensions {Lz~ 0.60 and not 0.90 mm.) 
and its smaller and more numerous tremopores. 
It differs from M etradoUum dissimile , in which the rimule-spiramen is vaguely 
symmetrical, in the absence of zooecia with spiramen, and in the somewhat smaller 
dimensions (Lz= 0.60 and not 0.76 mm.). 
Occurrence. — Middle Jacksonian (Castle Hayne limestone) : Wilmington. North 
Carolina (very common). 
C otypes.- — Cat. No. 64119, U.S.N.M. 
METRADOLIUM OBLIQUUM, new species. 
Plate 57. figs. 4-10. 
Description. — The zoarium is free, bilamellar, erect; the fronds are flat, bifur- 
cated ; the two lamellae are back to back and inseparable. The zooecia are elon- 
gated, very little distinct ; the frontal is thick, convex ; it is formed of a tremocyst 
with tubules surmounting an olocyst, which is very thin and finely perforated with 
corresponding pores. The apertura is oblique, suborbicular ; the peristomice is 
formed of a subcircular anter with poorly defined outlines and of an unsymmetrical 
rimule-spiramen oblique with respect to the zooecial axis. The ovicell is globular, 
salient, hyperstomial. largely open into the peristomie, deeply embedded in the distal 
zooecium; it is covered with tremopores like the frontal; the peristomice is large, 
transverse, in the form of a lunar crescent, of which the convexity is proximal. 
Two avicularia are symmetrically placed on each side of the rimule; the larger is 
salient, transverse, oval, provided with a pivot, its beak turned outward. 
Measurements.— Apertura 
(interior) 
Zooecium 
j7tf=0.15 mm. 
iZs=0.70-0.80 mm. 
\lz= 0.40-0.50 mm. 
Peristomice 
(exterior) 
= 0.15 mm. 
