744 SYSTEMATIC PALEONTOLOGY 



Description. " Zoarium encrusting, consisting of one or more layers ; 

 surface under a low power of magnification presenting a decidedly rough 

 aspect. Zocecia varying from ovate-hexagonal to subrhomboidal, indis- 

 tinct externally, arranged more or less irregularly, though the rows are 

 more regular than may appear at first sight ; about six in 2 mm. Aper- 

 tures rounded or subquadrate, 0.13 mm. in diameter, rendered oblique by 

 the elevation of the more or less strongly swollen posterior margin and 

 the depression of the anterior part. The central portion of the raised lip 

 forms a " mucro " of greater or less thickness and prominence, the same 

 hiding a minute central tooth beneath it, and forming with the rest of 

 the thickened portion of the lip a more or less obscure resemblance to the 

 figure W. Behind the lip, the surface slopes rapidly and in the most nearly 

 perfect example is granulose. In the depressed space in front of the 

 aperture there are, normally, three small raised avicularia (? vibracula), 

 while a few larger avicularia, differing further from the others in being 

 divided into two unequal parts by a cross-bar, are scattered without order 

 among the zocecia. Ocecia are not often seen. When present they occupy 

 the depressed space in front of the aperture, are cucullate, about as large 

 as the zocecial aperture, and usually bear a furrow running from the 

 summit to the concave edge." Ulrich, 1901. 



The encrusting zoarium, mucronate aperture, and the small raised 

 avicularia will serve for the recognition of this species. 



This species is not uncommon in the Vincentown limesand of the Upper 

 Cretaceous at Vincentown, New Jersey. Common at the same horizon in 

 Delaware. The species also occurs rarely in the Lower Eocene (Aquia) 

 at Upper Marlboro, Maryland. 



Occurrence. RANCOCAS FOEMATION. South side of Appoquinimink 

 Creek between mill-dam and Odessa, and at Noxontown Millpond, Dela- 

 ware. 



Collection. Maryland Geological Survey. 



