BRYOZOAN FAUNA OF VINCENTOWN LIMESAND 51 



transverse; the poster is rectilinear and separated from the anter 

 by two minute pseudocardelles placed very low ; the distal peristome 

 is thin, salient, probably ornamented with small spines. The ovicell 

 is hyperstomial, buried in the distal zooecium, closed by the oper- 

 culum, large, globular, smooth, elongated, decorated with a salient, 

 median, longitudinal crest. The vibracula are interzooecial, small, 

 irregularly scattered, but often grouped around the apertures. 



Measurements. — 



. [Lz= 0.3-0.45 mm. . [Aa=0.05 mm. 



Zooecia ( ?55 = 0.25-0.3 mm. A P ertura |/« = 0.00-0.07 mm. 

 30-32 zooecia in 4 sq. mm. 



Structure. — The distal extremity of the vibracula is salient, and 

 as a result the orifices are oriented obliquely toward the proximal 

 portion of the zooecia. This arrangement is not always constant. 



The zooecia have a small proximal gymnocyst, although almost 

 always it is hidden by the ovicell or by the vibracula. 



It is difficult to interpret the irregularity of the vibracula. There 

 are always at least two to a zooecium. Often a third is added if 

 a new series forms. Finally, certain of them appear to replace 

 zooecia that cannot develop normally because of irregularity of 

 gemmation. 



The granules which decorate the costules correspond perhaps to 

 the lumen pores. 



Occurrence. — Vincent own limesand : Very rare at Noxontown Mill- 

 pond, Del. 



Holotype.— U.S.N. M. No. 73930. 



PLIOPHLOEA VENTRICOSA, new species 



Plate 11, Figures 6-11 



Description. — The zoarium encrusts Bryozoa or shell fragments; 

 it may also be free and formed of hollow multilamellar cylinders; 

 the external lamella is composed of subcolonies arising from a false 

 ancestrula. The zooecia are distinct, separated by a deep furrow, 

 elongated, elliptical, ventricose, often restricted in back. The fron- 

 tal is convex and formed of a gymnocyst of variable size and of 

 a median costulated area; the costules are short, wide, 8 to 11 in 

 number, convex, salient, granulated, united except at the end; the 

 apertural bar is thick, crescentic, enlarged laterally. The aperture 

 is small, terminal, semielliptical, somewhat transverse; two minute 

 false cardelles placed very low in the vicinity of the proximal bor- 

 der separate the large anter from the poster. The ovicell is hyper- 

 stomial, embedded in the distal zooecium, closed by the operculum : 

 it is large, convex, smooth, with a quite salient median keel. The 

 zooeciules, large or small, are primoserial or arranged in chains 



