Corals and Brtozoans of the Lower Helderberg. 163 



This species can be distinguished from E. nebulosa (plate xvi, figs. 14-16), 

 to which it bears some resemblance, by its rhomboidal or hexagonal cells, with 

 equally thick walls ; equal length and width, and the absence of the regular 

 longitudinal arrangement of cells, which is characteristic of that species. 



Formation and locality. Lower Helderberg group, Schoharie, N. Y. 



FENESTELLA, Lonsdale. 

 Fenestella compacta, n. sp. 



(PLATE XVIII, FIGS. 1-3.) 



Bryozoum cup-shaped. Branches strong ; eight and nine in the space of five 

 mm. ; on non-poriferous side flattened, obscurely striated and much enlarged 

 below the bifurcations, which are infrequent. 



Dissepiments strong, from one-half to equal thickness of the branches ; seven 

 in the space of five mm., expanding at their junction with the branches ; rounded 

 and depressed on both poriferous and non-poriferous sides. 



Fenestrules oval or subquadrangular, width less than that of the branches. 



Cell-pores small, round, in two or three ranges ; sometimes the third range 

 extends but a short distance below the bifurcations, occasionally extending nearly 

 to the next bifurcation below ; distance of pores from each other equal to or 

 greater than the diameter, opening directly upward ; margins elevated, and 

 indenting the boarder of the fenestrule. 



Formation and locality. Lower Helderberg group, Clarksville, N. Y. 

 Fenestella arta, n. sp. 



(PLATE XVIII, FIGS. 4-9.) 



Bryozoum cup-shaped, undulating. Branches strong, varying in width ; from 

 five to nine in the space of five mm. ; on non-poriferous side round, frequently 

 slightly angular, apparently smooth, enlarging very much below the bifurcations, 

 being frequently double the width of the branches just above. 



Dissepiments from one-half to two-thirds the thickness of the branches imme- 

 diately above the bifurcations; six in the space of five mm., expanding at their 

 junction with the branches, angular on non-poriferous side, rounded and slightly 

 depressed on poriferous side. 



Fenestrules small, varying in form from subquadrangular to oval ; width from 

 one-fourth to two-thirds that of the branches, appearing much smaller and fre- 

 quently scarcely perceptible on poriferous side. 



Cell-pores in two and three ranges ; always three ranges immediately below the 

 bifurcation, the third range sometimes extending but a short distance, at others 

 nearly to the bifurcation below; pores small, round, or slightly oval; three in 

 the space of a fenestrule ; distance from each other equal to or greater than 

 their diameter, opening directly upward ; where there are three ranges of pores, 

 the openings of the two outer ranges are oblique to the axis of the branch ; 



