Corals and Bryozoans of the Lower Helderberg. 173 



This is a very distinctly marked species, and is easily recognized by its ex- 

 tremely slender dissepiments and square fenestrules. 



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



Fenestella (Hemitrypa) Nervia. 



(PLATE XXII, FIGS. 1-6, AND ? 9, 10.) 



Feii&tdla NervicL, Hall. Twenty-sixth Rep. N. Y. St. Mus. Nat. Hist., p. 93. 1874. 

 Hemitrypd prima. Hall. " " " " p. 98. 1874. 



Bryozoum broadjy spreading, funnel-shaped, undulating on a line with the 

 branches. Branches closely arranged, nine in the space of five mm. ; on non- 

 poriferous side rounded, apparently smooth, though better preseved specimens 

 may show striae ; bifurcations frequent, irregular. 



Dissepiments from one half to equal the thickness of branches, six in the space 

 of five mm., widening at their junction with the branches; on non-poriferous- 

 side on the same plane as the branches, on poriferous side deeply depressed. 



Fenestrules oval, generally from one-half to two-thirds the width of the 

 branches, length twice the width. 



Cell-pores in two ranges, opening, obliquely to the axis of the branch ; openings 

 small, oval or circular, three to four in the space of a fenestrule, counting those 

 opposite the dissepiment, generally one, sometimes two so situated ; margins of 

 upper portion of cell-pores distinctly elevated, of lower portion slightly elevated ^ 

 space between ranges of pores carinated, carina sharp, elevated equal to the 

 thickness of the branch, expanded above ; expanded portion finely striated and 

 having in the center a small sharp keel ; crests of carinse connected by a series 

 of narrow, angular and striated bars, about fourteen in the space of five mm. 



This species, in the study of more extensive collections, was found to include 

 the forms previously described as Hemitrypa prima. 



Formation and localities. Lower Helderberg group, two miles north of 

 Clarksville, N. Y., and at Schoharie. 



Fenestella Cleis, n. sp. 



(PLATE XXI, FIGS. 7, 8.) 



Bryozoum broadly cup-shaped. Branches closely arranged, moderately strong, 

 nine in the space of five mm. ; on non-poriferous side somewhat flattened ; 

 striated, striae granulose, strong, from three to five on a branch ; bifurcations 

 comparatively regular. 



Dissepiments six in the space of five mm., expanding at their junction with 

 the branches, on non-poriferous side on plane of the branches ; on poriferous side 

 depressed. 



Fenestrules small, oval, width from one-half to two-thirds the width of the 

 branches, length from once and one-half to a little more than twice the width. 



Cell-pores in two ranges, opening obliquely outward ; openings small, round, 

 three or four in the space of a fenestrule, distance from each other equal to 

 or greater than their diameter ; margins elevated ; space between ranges of 



