584 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
visible exteriorly and placed just in front of the labial mucro; it is hyperstomial, 
recumbent, somewhat supported on the distal zooecium; it is smooth and formed 
like the frontal of an olocyst under a pleurocvst. 
SHORT HEXAGONAL ZOOECIA. 
Measurements . — Apertura 
7<a=0.08 mm. 
7a=0.14mm. 
Zooecia 
[Z2=0.60mm. 
[73=0.40-0.50 mm. 
LONG ZOOECIA. 
Apertura 
A«=0.10 mm. 
?ffl=0.14 mm. 
Zooecia 
Lz= 0.64-0.7 0 mm. 
7s=0.50-0.60 mm. 
Variations. — The exterior peristomie is little visible by the illumination from 
above in our figures; it fs more accentuated under the microscope by illumination 
from below. The young zooecia have a complete peristome (figs. 20, 21) and the 
areolae are quite visible. On old zooecia the pleurocvstal calcification is intense in 
the vicinity of the areolae, so that the zooecia appear to be surrounded by a wide 
collar (figs. 18, 19). Sometimes in the interior of the peristomie there are two 
or three denticles ; their fragility is perhaps the cause of their rarity. 
Affinities . — The greater affinities of this species are with Perigastrella oscitans , 
and near the ancestrula confusion is possible. Perigastrella plana differs from it 
in its greater width (73=0.40-0.60 and not 0.60-0.40 mm.) ; in the oval, nonellip- 
tical form of the zooecia. and in the proximal border of the crenulated apertura. 
O cciumenee.— Vicksburgian (Marianna limestone) : West bank Conecuh Eiver, 
Escambia County, Alabama (rare) ; Murder Creek, east of Castlebury. Conecuh 
County, Alabama (common) ; near Claiborne, Monroe County, Alabama (very com- 
mon) ; one mile north of Monroeville, Alabama (very common) ; Salt Mountain, 
five miles south of Jackson, Alabama (common). 
Vicksburgian (Byram marl) : Bvram, Mississippi (rare). 
Cotypes. — Cat. Nos. 63918, 64324, U.S.N.M. 
PERIGASTRELLA? COSTIFERA, new species. 
Plate 100, figs. 12-17. 
Description. — The zoarium is incrusting cylostome bryozoa. The zooecia are 
distinct, elongated, fusiform, provided at their extremity with a long exterior 
peristomie; the frontal is somewhat convex and bordered laterally with widely 
spaced areolae ; it is formed of a pleurocyst with interareolar costules more or less 
long. The apertura, invisible exteriorly, appears orbicular and oblique. The 
peristomice is irregular, oblique, with four distal spines. The ovicell is small, 
hyperstomial, recumbent, opening into the peristome. 
Measurements . — Zooecia 
Lz= 0.35-0.45 mm. 
7.3=0.20-0.25 mm. 
Affinities. — On account of its orbicular orifice and its large peristomie, this 
species may be classed approximately in Lagenipora Hincks, 1880. Waters, in 1899, 
