148 BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 



Occurrence. — Oligocene (Antigua formation) : Rifle Butts, Antigua, Leeward 

 Islands (rare). 



Hahitat. — Shetland Islands. Waters ofl" Florida (185 meters) . 

 Plesiotype.— Cat. No. 68649, U.S.N.M. 



PORELLA REVEKSA Ulrlch and BaasU-r, 1904. 



Plate 2.3, figs. 5-10. 



1904. Lepralia 7 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 

 di\'ided 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 tlie 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. 



ir J \ 4. fAa=0.15mm. „ . fi2 = 0.45-0.55 mm. 



Measurements. — Apertura , „ , „ Zooecia , 



I7a=0.1.3mm. I fe = 0.25-0.30 mm. 



A reexamination of the type specimen shows tliis 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 tlie 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). 



CotyiJes and Plesiotype.— Cat. Nos. 68650, 68651, IT.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, 

 fig. 72. 



Mms«rmente.-Aperturaft^ = ^-24 ^"^^ Zooecia[^^ = 0.80-1.00 mm. 



lto = 0.20mm. 1 Z2= 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 



