34 
BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 
ACANTHODESIA OBLONGULA Ulrich and Bassler, 1904. 
Plate 10, figs. 1-3. 
1904. Membranipora oblongula Ulrich and Bassler, Bryozoa, Maryland Geological Survey, 
Miocene, p. 407, pi. 110, figs. 2-5. 
Description .—The zoarium incrusts shells. The zooecia are distinct, separated 
by a furrow of little depth, elongated, rectangular; the mural rim is rounded, regular, 
granular, ornamented by two large distal tubercles. The opesium is entire, elliptical, 
finely denticulated and provided with spicules of greater or less length. 
Measurements .—Opesia 
'/to = 0.40 mm. 
lo = 0.15 nun. 
Zooecia- 
Lz = 0.45-0.50 mm. 
lz = 0.25-0.30 mm. 
Variations. —The figures of Ulrich and Bassler are incomplete as the tubercles 
have not been restored fully enough. On Plate 10 we reproduce a better photograph 
of the type (fig. 1). Sometimes the tubercles are joined and form a single large 
distal tuberosity (fig. 2). The micrometric measurements vary according to the 
specimens and even on the same specimen they are irregular. The zooecia giving 
rise to a new series are larger according to the rule in the genus. 
Affinities. —This species differs from Membranipora jiabellata Canu, 1904, in 
the presence of spicules and in the larger micrometric measurements. It differs 
from Acanthodesia savarti Audouin, 1826, in the presence of large distal tubercles. 
Occurrence.- —Miocene (Calvert formation): Plum Point, Reeds, and Chesapeake 
Beach, Maryland (common). Miocene (Choptank formation): Jones wharf, Paw¬ 
paw Point, Dover Bridge, etc., Maryland (rare). 
Plesiotype. —Cat. No. 68433, U.S.N.M. 
ACANTHODESIA RECTANGULARIA, new species. 
Plate 9, fig. 11. 
Description .—The zoarium incrusts oyster shells. The zooecia are distinct, 
elongated, rectangular; the mural rim is thin, salient; the cryptocyst is deep, 
short, a little convex. The opesium is large, oval, terminal. 
Measurements. —Opesia- 
ho = 0.35 
lo = 0.20 
mm. 
mm. 
Zooecia- 
\Lz = 0.50-0.55 mm. 
[ Zz = 0.30-0.35 mm. 
Affinities.—On certain isolated zooecia we have been able to observe some 
spines and even traces of the serrate proximal denticle. In spite of appearances 
of our figure, which is incomplete because of the disappearance of the spines, this 
species belongs really to the genus Acanthodesia. It is well characterized by the 
rectangular’form of its zooecia. 
Occurrence. —Miocene (Yorktown formation): 3 miles southwest of Petersburg, 
Virginia (rare). 
Holotype. —Cat. No. 68434, U.S.N.M. 
