BRYOZOAN FAUNA OF VINCENTOWN LIMESAND 73 



Variations. — The micrometric variations are great, especially in 

 the vicinity of the ancestrula, which is here a small ordinary 

 zooecium measuring only 0.2 mm in length. 



The zooeciules are still more variable, for there are long ones 

 measuring 0.5 mm and small examples scarcely 0.2 mm in length. 

 They are almost always oriented distally, but there are some cases 

 of curious and unexpected inversions. They are generally isolated, 

 although sometimes there are groups of 3 to 6 adjacent zooeciules; 

 on other parts of the colony they form small linear series of 3 to 4 

 successive zooeciules. 



Many of the zooecia are covered by a second incomplete pellicle in 

 structure analogous to that of the primitive frontal. The two frontal 

 pores are difficult to discern, for they disappear frequently in fos- 

 silization. It is necessary to tint the specimens blue in order to dis- 

 cover them more easily. 



Among the Cretaceous fossils, the species of the Cribrimorph 

 group of Distansescharella D'Orbigny, 1852, have an aspect close to 

 that of the Hippothoidae. Their differentiation is difficult and is 

 a constant source of error of determination. 



It is possible to recognize perhaps in the genus Diplotresis the an- 

 cestor of the Tertiary-Recent genus Haplopoma Levinsen, 1909, in 

 which the ascopore is simple, both of them being derivatives of 

 Cribrimorph ancestors. 



Occurrence. — Vincentown limesand: Rare at Vincentown, N.J., 

 and 2 miles southwest of Odessa, Del. 



Holotype.— U.S.N.M. No. 52607. 



Family ACROPORIDAE Canu, 1913 

 Genus BEISSELINA Canu, 1913 



BEISSELINA LABIATA Gabb and Horn, 1862 



Plate 19, Figures 7-13 



1862. Crescis labiata Gabb and Horn, Journ. Acad. Nat. Sci., Philadelphia, 



ser. 2, vol. 5, p. 177, pi. 21, fig. 69. 

 1907. Porina labiata Ulrich and Bassler, in Weller, Geol. Survey New Jersey, 



Paleontology, vol. 4, p. 350, pi. 26, figs. 1-0 (bibliography). 

 1920. Beisselina labiata Canu and Bassler, U.S. Nat. Mus. Bull. 106, p. 324, 



pi. 7, fig. 14. 



Description. — The zoarium is free, bilamellar, formed of two op- 

 posed inseparable lamellae; the branches are compressed, rather 

 wide, dichotomous, elliptical in cross section; the base is attached 

 to other free Bryozoa. The zooecia are indistinct, elongated, ar- 

 ranged in quincunx ; the frontal is hidden under the avicularia visi- 

 ble exteriorly; it bears a large ascopore, little removed from the 

 aperture and opening in the interior of the zooecium below the oper- 



