MARYLAND GEOLOGICAL SURVEY 407 



ridges, considerable clusters of apertures occur, while other groups may 

 not contain more than three or four cells. Occasionally an irregular 

 radial arrangement of the ridges is apparent. About four zooecial aper- 

 tures in 1.0 mm. 



The ridges or as they may be more appropriately called, the elevated 

 bundles of zooecial apertures, are smaller and more interrupted, and the 

 deep interspaces relatively greater than in any other species of Tlieonoa 

 known to us. Excepting that the radial arrangement of the ridges is 

 much less apparent and the zoarium thicker, T. glomerata presents con- 

 siderable resemblance to Kololoplios terquemi (Haime) Gregory, and it 

 would not require any very essential modification of Gregory's proposed 

 genus to receive it. But as there is some question in our minds as to the 

 necessity of Kololoplios and less doubt concerning the intimate relations 

 cf our species to Theonoa we have thought it better, for the present at 

 least, to place it into the old genus rather than to modify the new genus 

 in a direction probabty not acceptable to its founder. 



Occurrence. — St. Mary's Formation. St. Mary's River. 



Collection. — Maryland Geological Survey. 



Order CHILOSTOMATA Busk. 

 Family MEMBRANIPORID^. 



Genus MEMBRANIPORA Blainville. 



Membranipora oblongula n. sp. 



Plate CX, Figs. 2, 3, 4, 5. 



Description. — Zoarium incrusting, forming delicate expansions often 

 of considerable extent over shells of mollusca and other foreign objects; 

 occasionally in superimposed layers. Zooecial apertures arranged in 

 longitudinal series, usually elongate, occupying the entire opesium, the 

 length often nearly or quite twice the width; when normally developed, 

 elongate, ovate or subquadrate but contingencies of growth and develop- 

 ment cause many variations without, however, ever seriously affecting the 

 general plan of the specific characteristics; measuring longitudinally 10 

 or 11 in 5 mm., transversely the average is about 10 in 3 mm. Wall vary- 

 ing in thickness, usually about two-thirds the width of the opesium. rarely 



