NORTH AMERICAN EARLY TERTIARY BRYOZOA. 489 



Finally, the avicularian zooecia are rather frequent: they are characterized 

 liy a very large opening. narrowed in its median part. We know that the operculum 

 is replaced there by a mandible and that the polypide has disappeared by histolysis. 



Occurrence. Middle Jacksonian (Castle Hay ne limestone) : Wilmington, North 

 Carolina (rare) ; near Lenuds Ferry, South Carolina (rare). 

 .C&t. No. r4l.V>. U.S.N.M. 



PORELLA ABDITA, new species. 



Plate 65, figs. 1-3. 



Description. The zoarium is large, bilamellar, and formed of two lamellae, 

 back to back, and inseparable. The zooecia are indistinct: the frontal is convex 

 and formed of a tremocyst with irregular pores. The peristomice is orbicular or 

 elliptical. The median avicularium is very small, buried in the thickness of the 

 tremocyst, opening in the peristomie, hardly visible exteriorly. Often a small 

 adventitious avicularium is placed in the vicinity of the peristomice. 



,, . thpe=0.20mm. . [7,2=0.70-0.75 mm. 



Mi axurements. Peristomice L Zooecia , 



\lpe=0.15 mm. |/~=0.30-0.3o mm. 



Affinities. We have collected only a small number of specimens and it is 

 possible, therefore, that they are related to another species of which they may be 

 the strongly calcified representatives. This is, in fact, the habitual variation in 

 Porella dent iculif era and Porella jacksonica. To be certain of the identification 

 with the latter species it TV ill be necessary to find a greater number of specimens 

 in the same localities. 



Occurrence. Upper Jacksonian (Ocala limestone) : Alachua. Florida (rare) ; 

 9 miles north of Ocala, Florida (rare). 



t'otypes.Cnt. Nos. G4154. G4155, U.S.N.M. 



PORELLA PORTENTOSA, new species. 



Plate 04, figs. 10-23. 



Description. The zoarium is bilamellar; the fronds are flat or a little un- 

 dulated. The zooecia are distinct, quite elongated, tubular; the frontal is convex 

 and formed of a tremocyst with large tubular pores, supported by a very thin, 

 perforated olocyst; the tubules have thick walls and are separated from one 

 another. The apertura is semilunar, with the proximal border convex; the peri- 

 stome is very thin, hardly salient. The ovicell is much embedded in the distal 

 zooecium, hardly prominent; its frontal is a perforated area: the ovicell is hyper- 

 stomial and opens into the peristomie. The avicularium is placed entirely within 

 the peristomie. 



. lhpe=0.nmm. . \L*=Q.SO-0.90mm 



Measurements. Peristomice \ ^ Zooecia , 



I ipe=Q.I2 mm. 1/2=0.26 mm. 



Variations. This species is quite remarkable. The tubules are not adjacent 

 and are separated from each other; this results in the frontal having a fantastic 

 aspect which is impossible to describe. When these tubules are adjacent (figs. 11, 



