BRYOZOAN FAUNA OF VINCENTOWN LIMESAND 79 



Family ESCHARELLIDAE Levinsen, 1909 

 Subfamily Peristomellae Canu and Bassler, 1917 



Genus EXOCHELLA Jullien, 1888 



EXOCHELLA SEPTENTRIONALIS, new species 



Plate 17, Figures 2-5 



1907. Hucronella pumila (part) Uliuch and Bassler, in Weller, Geo! Surv. 

 New Jersey, Paleontology, vol. 4, p. 355, pi. 26, fig. 16. 



Description. — The zoarium encrusts C oscinopleura, fragments of 

 sea-urchins, and shells; it is small. The zooecia are distinct, sepa- 

 rated by a thin thread placed at the bottom of a deep furrow, little 

 elongated, swollen, ensiform; the frontal is convex, smooth, bor- 

 dered by some small areolar pores, little visible, and terminated by 

 a salient mucron, which is erect, flat, wide, bifid, and hiding the 

 aperture. The aperture is semielliptical, transverse, little visible, 

 concealed at the bottom of the locella ; the peristome is thin, little 

 salient, garnished with 2 small distal spines and with 2 lateral ones. 

 The ovicell is hyperstomial, resting on the distal zooecium, widely 

 open in front of the mucron, not closed by the operculum. On each 

 side of the aperture there is a small avicularium with pivot, trian- 

 gular, oriented distally. The ancestrula is small, membraniporoid 

 or not. 



Measurements. — 



„ . fZs = 0.45 mm. . \ ha=0.08 mm. 



Zooecia ^ 7 Apertura- nionir 



^2 = 0.36 mm. \la = 0.12-0. 15 mm. 



Variations. — The ancestrula r zooecia are much smaller than the 

 marginal zooecia and as the zoaria are very small, the number of 

 cells to the square millimeter is quite variable; it is 12 around the 

 ancestrula and 5 or 6 only on the zoarial margins. There are only 

 two avicularia on the wide marginal and ovicelled zooecia and none 

 at all on the nonovicelled ones. The narrow ovicelled zooecia have 

 only a single avicularium. 



The well-developed nonovicelled zooecia have 4 spines, but the 

 ancestrular zooecia have only 2. On the ovicelled zooecia the spines 

 are replaced by the avicularia. 



The mucron is well developed only on the ovicelled zooecia. On 

 the others it is smaller, less salient, and not bifid. 



The ancestrula appears very variable. It is a very small ordinary 

 zooecium without avicularia. However, we have figured a colony 

 on which the ancestrula is reduced to an apertural portion accom- 

 panied by four small avicularia. 



Affinities. — Exochella septentrional is differs notably from the other 

 species of the genus in the absence of large areolar pores and in the 



