CORALS AND BRYOZOA. 43 



others ; very closely arranged in quincunx, nearly in contact : margins very 

 thin, scarcely elevated above the surrounding surface. Interapertural space 

 flat; granulose. 



The general appearance and arrangement of the cell apertures will distinguish 

 this species from any similar form in the same horizon. 



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



Thamniscus? Nysa. 



PLATE XXn, FIGS. 31, 32, 47, 48. 



ThamnUcux Nysa, Hah. Thirty-second Kept. N. Y. State Mus. Nat. Hi.st., p. 175. 1879. 



" " var. Hall. Thirty-second Rept. N. Y. State Mus. Nat. Hist., p. 176. 1879. 



" " " Repoi-t of State Geologist for 1882. Expl. pi, 22, figs. 31, 32. 1S83. 

 " Hall. Report of State Geologist for 1882. Expl. pi. 22, figs. 47, 48. 1883. 



ZoARiUM ramose, solid. Bifurcations frequent; branches 1 mm. in diameter, 

 very slightly enlarging Ijefore bifurcation ; frequently curved. Non-cellulif- 

 erous face ob.scurely striated. Cells tubular, opening directly outward; 

 diameter of apertures .15 mm. ; disposed in oblique transverse rows ; distance 

 between rows equal to the diameter of an aperture, the apertures forming the 

 transverse rows nearly or quite in contact : margins thin, strongly elevated. 



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



FENESTELLA (Miller), Lonsdale. 1839. 

 Fenestella crebripora. 



PLATE XX, FIGS. 1-3. 



Feiumtdla erebrlpora. Hall. Twenty-sixth Rept. N. Y. State Mus. Nat. Hist., p. 95. 1874. 



Thirty-second Rept. N. Y. State Mus. Nat. Hist., p. 167. 1879. 

 " " •• Report of State Geologist for 1882. Expl. pi. 20, tigs. 1-3. 1883. 



Bryozoum infundibuliform. Branches slender, rounded or sub-angular, marked 

 by very fine striae which are often indistinct. Bifurcations distant from 

 4 to 10 mm. Width of interstices greater than that of the branches. Dis- 

 sepiments slender, often oblique, on the same plane as the branches, five 

 in the space of 5 mm. Fenestrules sub-quadrangular, often rhomboidal, 

 width usually about one-half the length. 



