XORTH AMERICAN EARLY TERTIAEY BRYOZOA. 145 



form and the nonregularity of the area of the ovicell. This is therefore an inter- 

 mediate form between Aldcr'ma intl/cllis 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 Jacksoninn (Moodys marl) : Jackson, Mississippi (very 

 rare) . 



Holotype.C&l. 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. 



Variations. "We possess only the single figured specimen, which is incom- 

 plete. Maity of the zooecia are regenerated. It is closely related to M ' embranipora 

 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). 



Ho7otype.Cat. No. 6392-i, U.S.N.M. 



Genus CALLOPORA Gray, 1848. 



1S4S. Callopora GRAY, List British Animals British Museum, Centroniae, pp. 109, 146. 

 1903. Callopora NORMAN, Notes on Natural History East Pinmark, 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 embranipora} 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 embranipora lineata group and the M. tenm- 

 rostri-s 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 



