84 BULLETIN 16 5, UNITED STATES NATIONAL MUSEUM 



Structure. — The longitudinal section shows thick frontal walls. 

 The ovicell is buried in the interior, and since it is placed below 

 the distal avicularium it is wholly invisible exteriorly. The ovicell 

 is thus visible only in thin sections. There is no peristome on the 

 young zooecia, but on the old cells there is one formed by the thicken- 

 ing of the frontal walls. 



The two lamellae of the zoarium are inseparable, and the zooecia 

 of each of these are placed exactly in front of the zooecia of the 

 other lamella. This symmetrical arrangement is perfect. 



The transverse section is elliptical, and there are no zooecia along 

 the edges of the zoarial branches. 



Affinities. — The presence of the lyrule seems to indicate that this 

 species belongs to the Smittinidae, for which reason Ulrich and 

 Bassler, 1907, referred it to Mucronella Hincks, 1877. But in this 

 genus the ovicell is not closed by the operculum and the ovicell is 

 not hidden. We prefer, however, to classify Psilosecos in the 

 Reteporidae for the reasons just given. 



Monoporella angustidens Levinsen, 1925, from the Danian of Faxe 

 has been well studied by its author. It is smaller and rarer and we 

 prefer to choose the American species as the genotype because it is 

 more abundant, larger, and its interior structure is known. 



Acanthionella oecioporosa Canu and Bassler, 1920, from the 

 Claibornian of Alabama seems to belong to this new genus. 



Occurrence. — Vincentown limesand: Mullica Hill, N.J. (Gabb and 

 Horn) ; not uncommon at Vincentown and near Blackwoodstown, 

 N.J. 



Plesioty pes.— U.S.N. M. No. 73902. 



Family CELLEPORIDAE Busk, 1852 



Genus ACANTHIONELLA Canu and Bassler, 1917 



ACANTHIONELLA TYPICA Gabb and Horn, 1860 

 Plate 16, Figures 1-7 



1860. Cellepora typica Gabb and Hokn, Proc. Acacl. Nat. Sci. Philadelphia, 



vol. 12, p. 366. 

 1907. Mucronella typica Ulrich and Bassler, in Weller, Geol. Surv. New Jersey, 



Paleontology, vol. 4, p. 353, pi. 26, figs. 12, 13 (bibliography). 

 1907. Mucronella aspera (part) Ulrich and Bassler, in "Weller, ibid., p. 355 



(not pi. 26, figs. 14, 15). 



Description. — The young zoarium encrusts the debris of shells and 

 C oscinopleiu-a ; it develops next into free compressed branches more 

 or less wide, dichotomous, formed of two lamellae placed back 

 to back, inseparable. The young zooecia are distinct, separated by 

 a furrow, elongated, oval, capitate; the frontal is convex, smooth. 



