Lower Helderberg Bryozoa and Corals. 99 



rib. Pores moderately large, in two ranges on the lateral branches, 

 with three or more on the midrib (not fully determined). 



Length of the longest specimen seven-tenths of an inch, imperfect 

 at both extremities ; width, including lateral branches, one-tenth of 

 an inch, four of them in length equal to the entire width of the 

 frond. 



Formation and locality. — On limestone surfaces of the Lower 

 Helderberg group, at Schoharie, New York. 



Genus ESCHAKOPORA Hall. 1847. 

 (Not ESCHAEIPORA D'Orh. 1851.) 



ESCHAKOPOKA TENUIS 71. Sp. 



Bryozoum growing in thin, elongate, narrow stipes, with parallel 

 margins, and celluliferous on both sides. Cells arranged in longitu* 

 dinal rows (eighteen rows counted in one specimen), the marginal 

 rows largest ; the cells of the outer row situated a little in advance of 

 the next within it, and so on to the central row, where the order is 

 reversed, so that the transverse rows of cells run obliquely down- 

 wards to the center from both margins. Cell apertures rhomboidal 

 or obscurely liexagonal and opening upwards ; the partitions between 

 them sharp on their outer edges. The cells from the opposite sides 

 of the stipe reach to the thin dividing epitheca in the center, and 

 are inclined to the axis at a very low angle ; the whole thickness of 

 the stipe is seldom more than two-hundredths of an inch; breadth 

 one-sixth of an inch. The longest stipe which we have seen is nearly 

 three inches, gradually narrowing from the middle upward. 



This species differs from all others of the type yet seen, in its great 

 tenuity, differing extremely from those of the Trenton limestones 

 which are often nearly as thick as wide. 



Formation and locality. — In shaly limestones of the Lower Hel- 

 derberg group ; Albany and Schoharie counties. New York. 



EsCHAKOPORA NEBULOSA n. Sp. 



Bryozoum forming thin, flat, elongate expansions, celluliferous on 

 both sides. Cell apertures quadrangular, length scarcely exceeding 

 the width, in parallel rows of contiguous ranges slightly alternating 

 with each other ; longitudinal partition walls thin, rounded on the 

 edges, transverse partitions more slender and usually not elevated to 

 the same plane, rising from the central epitheca and gradually curv- 



