CLI^^o^ grottp. 



51 



where they are but a thin straight bar. This also gives the fenestrule a larger or longer space, 

 and conduces in part to the variable form. Lateral pressure, however, seems often to have 

 narrowed these spaces, and they are also of variable size in their perfect condition. 



Fig. 4 a. The base of a frond, showing the external poriferous face. 

 Fig. 4 6. A portion of the same enlarged. 

 Fig. 4 c. The uon-poriferous face of a portion of a frond- 

 Fig. 4 d. Several of the fenestrules near the base enlarged, showing distinctly the oval form. 

 Fig. 4 e. Several of the fenestrules enlarged (from a portion of the surface which has been worn 



down), showing a quadrangular form. 

 Fig. 4jf. A surface of stone, preserving the impression of the poriferous and non-poriferous faces 



of this coraL 

 Fig. 4 g-. A portion enlarged, showing the thin sharp lines of impression of the branches of the 



poriferous face. 

 Fig 4 h. Enlargement of the spaces filling the fenestrules on the non-poriferous face. 

 Figs. 4 2, A:, Z, in. Similar enlarged portions of the impressions of the two faces of the coraL 



Position and locality. This species is very abundant in the green shale above the ore bed 

 at Wolcott furnace ; also in the semi-calcareous portions of the rock, associated with the ore 

 bed below the shale. It is abundant likewise at Ontario in Wayne county, and it occurs at 

 Rochester, Reynale's basin, and Lockport, New- York ; and at Flambororough Head, Canada 

 West. {State Collection.) 



433. 2. FENESTELLA TENUIS. 



Pl. XIX. Fig. 5 a, h, c. 



Frond much expanded, thin and slender ; branches small, roundish, dividing at irregular in- 

 tervals ; bars small, thin, not curved or enlarging ; fenestrules oblong, quadrangular or sub- 

 rhomboidal ; length and breadth about as five to three ; poriferous face of branches carinate, 

 with a row of small round prominent pores on each side of the thin carina, and distant from the 

 margins of the branch ; about four pores to each fenestrule ; sometimes a pore upon the trans- 

 verse bar distant from the branch. Fenestrules about 6 in three lines longitudinally, and 12 in 

 the same space transversely. 



This species differs from the last in the more slender branches, the size and form of the 

 openings, and other more minute details. There is little tendency to the oval form in the fenes- 

 trules. The bars are scarcely enlarged as they join the branches ; and their direction is usually 

 a little oblique, giving a sort of rhomboidal form to the fenestrule. The poriferous side of the 

 branches differs equally from the last in the thin carinate edge being much lower, and the 

 transverse bars more prominent ; the pores are likewise smaller and more distant, and open 

 more directly outward. The upper or younger parts of the frond of F. prisca bear a more close 

 resemblance to this species on their non-poriferous face, than any other part of the coral. 



