-MAKYLAMJ (ii;u]-0(JlCAL SLliVEY 213 



fhistrella heleropora GaMi .-iiid Muni. Lcnj^Mli of /.oocciiiin 0.5 or U.G 

 111111.; width 0.'^') lo ().;!!» mni. Tliu spi'dincn dcscriljed sliows a single 

 ffll dill't'rino- I'l'dni tlic it-i in hcing closed, a ((nivex cover, at tiie ii]j])er 

 CAtiTinit y (if which a scini-circidar iiii |ircssi()ii is disliii;.;-idshahlt', extend- 

 ing over the wlidh'. 



Ocairreiicc. — Aquia FoinrA'rrox. Upper Marlboro. 



Collection. — Maryland Geolngieal Survey. 



MinrnKAxiPORA angusta n. sp. 



Plate LX, Figs. 5, Ck 



Description. — Among the material from Upper Marlboro, there are 

 several specimens of a delicate Memhranipora that, on account of their 

 imperfection and fj'agile nature, it may be risky to distinguish as a new 

 species. However, as it is easily recognized and may ^irove useful in 

 stratigraphic studies the writer has ventured to name it as above. The 

 zooeeia are shallow, elongate, elliptical, hexagonal or rhomboidal and 

 separated except in young stages by a thin tuberculated wall common to 

 adjoining cells (i. e. there is usually no depressed dividing line between 

 the zooeeia). The inner portion of the wall is much thicker than the 

 outer, so that the mouths of the connecting pores, of which there are at 

 least six on each side and one or two at each end, are clearly shown in a 

 view of the front. Two specimens have cucullate ooecia as shown in 

 Figure 5, and on all an occasional small oval or rounded and slightly 

 raised avicularium may be noticed. The zooeeia are about 0.4 mm. 

 long and 0.2 mm. wide. M. angusta apparently belongs to the M. 

 I i neat a group of AYaters. 



Occurrence. — Aquia Formation". Upper Marlboro. 



Collection. — Maryland Geological Survey. 



Genus REPTOFLUSTRELLA d'Orhigny. 



Eeptoflusteella heteeopoea Gabb and Horn. 



Plate LX, Figs. 8, 9. 



Beptoflustrella heieropora Gabb and Horn, 1862, Jonr. Acad. Nat. Sci. Pbila., 2nd 

 ser., vol. Y, p. 162, pi. xx, tig. 50. 



Description. — ''■' Colony encrusting in irregular patches. Cellules in a 

 single layer, placed Avith but little regularity, but with a tendency to 



