CORALS AND BRYOZOA. 15 



Ptychonema Helderbergi^. 



PLATE IX, FIGS. 10, 17. 



Chwtetes Helderhergiw, Hai.l. Twenty-sixth Rept. N. Y. State Mus. Nat. Hist., p. 110. 1874. 

 Not Favosites helderberffiw, H.vll. Twenty-sixth Rept. N. Y. State Miis. Nat. Hist., p. 111. 1874. 

 Favosites inerpectans. Hall. Thirty-second Rept. N. Y. State Mus. Nat. Hist., p. 14B. 1880. 

 CJicetetes ffelderlerguB, " Report of State Geologist for 1882. Expl. pi. 9, tigs. 16, 17. 1883. 



CoRALLUM ramose; diameter of the branches 10 mm. Cell tubes polygonal, 

 arising from the center of the branch and very gradually diverging until within 

 1 min. irom the surface when they aljruptly turn outward, the .apertures being 

 parallel with the surface; length reaching 15 mm.; diameter of apertures of 

 larger cells from .50 to .65 mm. There are numerous intercalations of young 

 cells whose apertures have a diameter of from .20 to .25 mm. Exterior of 

 cell walls strongly and regularly corrugated ; about fifteen in the space of 5 

 mm. The corrugations sometimes form nodes at the angles of the walls. 

 Septa thin, distant in the lower portion of the tube, becoming more numerous 

 near the surface. 



Formation and localities. In the shaly limestone of the Lower Helderberg 

 group, at Catskill creek, near Clarksville, and at Schoharie, N. Y. 



TREMATOPORA, Hall. 1852. 



TrEMATOPORA ? (TrEMATELLA ?) CORTICOSA. 



PLATE X, FIGS. l-IO ; PLATE XHI, FIG. 4 ; AMD PLATE XXUI, FIG. 20. 



Trematopora corticom. Hall. Twenty-aixth Rept. N. Y. State Mus. Nat. Hist., p. 115. 1874. 

 Chatetet corticom. Hall. Thirty-second Rept. N. Y. State Mus. Nat. Hist., p. 149. 1880. 

 Trematopora (Cluftetes) corticosa. Hall. Report of State Geologist for 1882. Expl. pi. 10, figs. 1-10 ; pi. 



13, fi)r. 4. 1883. 



CoRALLUM ramose, solid ; branches sometimes frequent ; at other times distant ; 

 often diverging at an angle of ninety degrees; diameter from 4 to 5 mm. 

 Cells tubular, polygonal ; arising from the center of the branch, gradually 

 diverging until within a short distance of the surface, when they abruptly 

 turn outward ; diameter .'25 mm. Walls thin, sometimes transversely 

 wrinkled. Septa comparatively strong, distant from each other about .50 



