MARYLAND GEOLOGICAL SURVEY 409 



the width of the opesium, with a median channel, the ring-like elevation 

 enclosing the opesium uniformly elevated except across the anterior end 

 where it is higher and obliquely arched and elevated beneath, probably 

 to form a cover for an ooecium, and is usually surmounted by a transverse 

 rib terminating at each end in a small rounded prominence. Rarely the 

 space of an ordinary zooecium is taken up by a cell having a thicker wall 

 and a smaller aperture varying from elongate to nearly circular, while 

 in one instance, a small cell with an oblique opening, narrowed distally, 

 is wedged in between three zocecia. 



This species probably belongs to the group of M. corhula as defined by 

 Waters. Compared with described fossil species M. fenestrata Reuss, 

 from the Miocene of Austria, seems the nearest. However, there are 

 good specific distinctions between them, the shape of the zocecia being 

 somewhat different, and the transverse depressed line between their ends 

 deeper and the ovicells less exsert in the Maryland species. 



Occurrence. — Calvert Formation. Eeed's. 



Collection. — Maryland Geological Survey. 



Membranipora caminosa n. sp. 

 Plate CXI, Figs. 3, 4. 



Description. — Zoarium adnate, forming a thin, single sheet of indefi- 

 nite extent. Zocecia arranged quincuncially, 6^ measuring longitudinally 

 and 7^ to 8^ diagonally, in 3 mm. Opesia subcircular, separated by one- 

 half to two-thirds their diameter; when the ooecium is wanting, a rim- 

 like border encloses the anterior half of the opening. Ooecia very high, 

 mth a rib across the top, and just in front of the latter a prominent 

 chimney-like tube or hollow spine projecting obliquely over the zooecium 

 next above. When the ooecium is broken away a semi-ovate or qua- 

 drangular concave space is uncovered between the ends of following 

 zocecia. The hollow tubule behind the zooecial aperture is always present 

 but it is usually worn down so as to appear as merely a thick- rimmed 

 pore. Where the zooecial arrangement is irregular or changed, a second, 

 or even a third tubule, each directed forward, may occur between three 

 zocecia. 



This species has a rather peculiar aspect, and we are at a loss to point 



