80 BULLETIN 16 5, UNITED STATES NATIONAL MUSEUM 



oral avicularia not placed on the adjacent zooecia. These differences 

 are not of generic order. 



All the recent and fossil species hitherto known occur in the tem- 

 perate zone of the Southern Hemisphere. So it is interesting to 

 note the extension of the genus in the warm zones of the Northern 

 Hemisphere. Canu, 1911, described two species from the Eocaneen 

 of Argentina, which is a horizon about equivalent to that of the 

 Vincentown limesand. Lepralia (Mucronella) neumayri Pergens, 

 1893, from the Maastrichtian of Limbourg, appears also to be an 

 Exochella. The figured specimen is not very good, but the author 

 states that the inferior part of the orifice bears in the middle a den- 

 ticulated prominence. If we are not mistaken, the genus Exochella 

 begins then in the Maastrichtian. 



Biology.— -This species of Exochella is organized to assure repro- 

 duction. The ovicelled zooecia are numerous ; they are accompanied 

 by protective adventitious avicularia and mucron. The colonies are 

 small and of short life ; they compensate for their precarious exist- 

 ence by their fertility. 



Exochella is the direct ancestor of Didymosella Canu and Bassler, 

 1920, by the fusion of the mucron with the proximal spines. The 

 latter genus remains purely equatorial and limited to warm waters. 



Occurrence. — Vincentown limesand: Not uncommon at Vincen- 

 town and near Blackwoodstown, N.J., and at Noxontown Millpond 

 and 2 miles southwest of Odessa, Del. 



Cotypes.—V.S.'NM. Nos. T3886, 73887. 



Family PHYLACTELLIDAE Canu and Bassler, 1917 



Genus PERIGASTRELLA Canu and Bassler, 1917 



PERIGASTRELLA EXSERTA Gabb and Ilorn, 1862 



Plate 20, Figures 1-3 



1862. Cellcpora exserta, Gabb and Horn, Journ. Acad. Nat. Sci. Philadelphia, 



ser. 2, vol. 5, p. 125, pi. 19, fig. 6. 

 1907. Monoporella exserta Ulrich and Bassler, in Weller, Geol. Surv. New 



Jersey, Paleontology, vol. 4, p. 349, pi. 25, fig. 567 (bibliography). 



Description. — The zoarium encrusts G oscinopleura and the debris 

 of shells. The zooecia are distinct, separated by a deep furrow, 

 large, little elongated, swollen, oval or barrel shaped ; the frontal is 

 convex, ornamented with small transparent granulations and sur- 

 rounded by small, scattered, areolar pores. The apertura is sub- 

 orbicular and placed at the bottom of a short peristomie; the peri- 

 stome is salient, thick, and fringed. The ovicell is recumbent, small, 

 globular, opening exteriorly or into the peristomie. Small dietellae 

 are present. 



