148 
BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 
Occurrence. —Oligocene (Antigua formation): Rifle Butts, Antigua, Leeward 
Islands (rare). 
Habitat. —Shetland Islands. Waters off Florida (185 meters). 
Plesiotype. —Cat. No. 68649, U.S.N.M. 
PORELLA REVERSA Ulrich and Basslcr, 1904. 
Plate 23, figs. 5-10. 
1904. Lepralia ? reversa Ulrich and Bassler, Maryland Geological Survey, Miocene, p. 426, pi. 113, 
figs. 1, 2. 
The original description is as follows: 
Zoarium forming parasitic patches, several centimeters in diameter and composed of a single 
layer, on shells. Zooecia oblong quadrate or subhexagonal, generally arranged in rather regular longitu¬ 
dinal and diagonally intersecting rows, each about 0.5 mm. in length and 0.3 mm. in width. Orifice 
rather large, rounded-quadrate, enclosed by a peristome of moderate thickness and elevation. Peristomes 
divided into two parts, anterior and posterior, the former either straight or slightly arcuate and not so 
prominent as the horseshoe-shaped portion enclosing the sides and proximal margins of the orifice. Distal 
extremities of the latter portion of the peristome often a little thickened and projecting slightly inward. 
Just behind the proximal border of the orifice there is constantly a rather small but prominently elevated 
and thick-walled avicularium, opening obliquely forward. Remainder of front zooecia with from one 
to three rows of large pores. Frequently adjoining zooecia are separated by a thin raised line. Ovicells 
moderately convex, rather large, with a central pore and one or two somewhat radially disposed marginal 
rows of smaller pores. When broken they leave a sharply defined concave space in front of the orifice, 
slightly exceeding the latter in size. 
The division of the peristome into two parts as described is unusual and produces the probably 
false appearance of a reversal of the ends of the operculum that has suggested the specific name. If it 
could be proved that the hinge of the operculum was really on the distal side of the orifice instead of the 
proximal, then this species would be distinct enough to justify the erection of a new genus for its recep¬ 
tion; but until this unusual condition can be demonstrated we think it well to regard it as related to 
such species as Lepralia pallasiana. We know of none resembling it closely enough to require unusual 
care in its discrimination. 
Measurements. —Apertura 
7to = 0.15 mm. 
to = 0.13 mm. 
Zooecia- 
'Lz = 0.45-0.55 mm. 
. to = 0.25-0.30 mm. 
A reexamination of the type specimen shows this species should be classed in 
the genus Porella. It is well characterized by its embedded aperture, by its in¬ 
fraoral avicularium, and by its ovicell perforated like the frontal. Finally the 
interior shows the parietal arrangement habitual in the Smittinidae (fig. 10). 
Occurrence. —Miocene (St. Mary’s formation): Cove Point, Maryland (rare). 
Miocene; Kuhns, Carteret County, North Carolina (rare). 
Cotypes and Plesiotype. —Cat. Nos. 68650, 68651, U.S.N.M. 
PORELLA COLLIFERA Robertson, 1908. 
Plate 38, figs. 10-15. 
1908. Porella collifera Robertson, The incrusting cheilostomatous Bryozoa of the west coast of 
North America, University of California Publications, Zoology, vol. 4, no. 5, p. 304, pi. 23, 
%. 72. 
... (7ta = 0.24 mm. „ . [1,2 = 0.80-1.00 mm. 
Measurements. —Apertura 7 - nn Zooecia 7 _ __ . 
1 l to = 0.20 mm. [ to = 0.50-0.60 mm. 
Variations. —The zoarium incrusts pebbles. The peristome is very salient 
especially in the proximal portion. The oral avicularium rests on a wide but little 
salient lyrule; it is often only visible by a suitable inclination of the preparation 
