NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
145 
form and the nonregularity of the area of the ovicell. This is therefore an inter- 
mediate form between Alderina imbelUs Hincks, 1860, and Alderina irregularis 
Smitt, 1872 ; perhaps it is an ancestral fossil form of those two recent species, one of 
which is boreal and the other equatorial. 
From this example the reader may judge of the great difficulties which often 
afflict us in the determination of the Membranipores. 
Occurrence. — Lower Jacksonian (Moodys marl) : Jackson, Mississippi (very 
rare). 
Holotype. — Cat. No. 63922, U.S.N.M. 
ALDERINA CRASSA, new species. 
Plate 29, fig. 7. 
Description. — The zoarium incrusts the radial plates of sea urchins. The 
zooecia are slightly elongated, distinct; the mural rim is very thick , convex, salient, 
granular. The opesium is elongated, elliptical, median. The ovicell is hyper- 
stomial. 
V aviations .- — We possess only the single figured specimen, which is incom- 
plete. Many of the zooecia are regenerated. It is closely related to Memhranipora 
perisparsa Novak, 1877. On our specimen one zooecium with a triple mural rim 
has twice undergone total regeneration. 
Occurrence. — Middle Jacksonian: Eutaw Springs, South Carolina (very rare). 
Holotype.- — Cat. No. 63924, U.S.N.M. 
Genus CALLOPORA Gray, 1848. 
1848. Callopora Gray, List British Animals British Museum, Centroniae, pp. 109, 146. 
1903. Callopora Norman, Notes on Natural History East Finmark, Annals and Magazine 
Natural History, ser. 7, vol. 11, p. 588. 
Front wall entirely membranous. Marginal walls more or less thickened and 
crowned with spines, which may be many or few. Ovicell globose, of good size, 
commonly with a rib across the front. Sessile avicularia with acute mandible at 
the bottom of the zooecium and above the ovicell or in a lateral position on one 
or both sides of the oral opening, or in both positions in the same species. Usually 
two pairs of lateral dietellae and one distal. (Norman.) 
Genotype. — Callopora ( M ernbranipora) lineata Linnaeus, 1758. 
Range. — Santonian-Recent. 
Nearly all the ovicells are provided in front with an area or more exactly 
with a callosity more or less granular, formed by the calcareous internal layer of 
the ovicell. 
This definition combines the M ernbranipora lineata group and the M. tenui- 
rostris group of Waters, which he defined: “Ovicells with rib; pore chambers 
usually one distal, four lateral ones; spines round the border. Vicarious avicu- 
laria.” 
55899— 20— Bull. 106 10 
