536 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
caused it to be classified in Schizoporclla. In 1914, the recognition of the ovicell 
system obliged Canu to create a new genus in which he classed in addition 
Metrardbdotos ( Eschara ) polymorphum Eeuss, 1869. 
This species made its appearance in Europe in the uppermost beds of the 
Priabonian; it does not exist in the bryozoan marl of the Priabonian. Its occur- 
rence is therefore valuable for the synchronism of the American formations, and 
it confirms the equivalence of the Vicksburgian with the Tongrian. It appears to be 
exterminated in the Upper Pliocene. 
Variations . — This species has not remained exactly identical, throughout its 
long geologic persistence. The ovicell of the specimens from the English Crag 
(Pliocene) is hardly costulate; the costules are quite visible and very clear in the 
French Miocene; they are finally very salient and quite vigorous in our American 
specimens. These variations do not seem to us of specific order, for the calcifica- 
tion of the zoaria depends much on the richness of the waters in lime. 
The restoration which we have attempted (fig. 1) indicates a ramose zoarium 
branching dicliotomously in the same plane; its total length seldom exceeds 3 or 4 
centimeters. 
The sinus of the apertura shows a small, very fragile lvrula whose function is 
unknown for it does not appear identical with the lvrula of Smittina. 
The zooecia are convex (fig. 3) or marginate (fig. 2) ; but always bordered 
with numerous and triangular, large areolae generally visible in the interior (fig. 6). 
The frontal of the ovicell (fig. 5) is very fragile and moreover often wanting 
on the fossils. The longitudinal section (fig. 10) is the habitual section of the 
endozooecial ovicells; the larvae ought to be very large. The orifice of the ovicelled 
zooecia is three times larger (Za=0.30 instead of 0.10 mm.) than the apertura of 
the ordinary zooecia. The tangential section (fig. 8) shows by its lateral reticula- 
tions and its sinous median line, the presence of a pleurocyst, reposing on the 
olocyst; but this appears very thin and is never seen exteriorly. 
Measurements . — Apertura 
| ka= 0.08 mm. 
0.10 mm. 
Zooecia 
s— 0.60 mm. 
= 0.30-0.36 mm. 
Maximum width of the fronds =2 mm. 
Occurrence . — Vicksburgian (Marianna limestone) : One mile north of Mon- 
roeville, Alabama (very common) ; near Claiborne, Monroe County, Alabama (com- 
mon) ; 24 miles north of Millry, Washington County, Alabama (rare) ; Vicksburg, 
Mississippi (common in the loiver beds). 
Geological distribution . — Priabonian of Transylvania and Galicia (Pergens). 
Latdorfian of Germany (Eeuss, Stoliczka). Eupelian of Germany (Eeuss). Chat- 
tian of Germany (Eeuss). Burdigalian of Spain (DeAngelis), of the Gard (Canu). 
Helvetian of Touraine (Michelin), of Spain (DeAngelis). Tortonian of Servia 
(Pergens), of Austria-Hungary (Eeuss), of Italy (Seguenza). Sahelian of Oran 
(Coll. Canu). Zancleen of Italy (Seguenza). Plaisancian of Italy (Seguenza, 
Neviani), of England (Busk), of Belgium (Van den Broeck). Astian of Italy (Se- 
