CORALS AND BRYOZOA. 
15 
Ptychonema Helderbergi,®. 
PLATE IX, FIGS. 10, 17. 
Chaitetes Hclclerberglcc, Hai.l. Twenty-sixth Rept. N. Y. State Mus. Nat. Hist., p. 110. 1874. 
Not Favosites Helderbergia ?, Hall. Twenty-sixth Rept. N. Y. State Mus. Nat. Hist., p. 111. 1874. 
Favosites inexpectans, Hall. Thirty-second Rept. N. Y. State Mus. Nat. Hist., p. 14(5. 1880. 
CJ/cetetes Helderbergia’, “ Report of State Geologist for 1SS2. Expl. pi. 9, figs. 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 mm. from the surface when they abruptly 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 ? (Thematella ?) corticosa. 
PLATE X, FIGS. 1-10 ; PLATE XIII, FIG. 4 ; AND PLATE XXIII, FIG. 20. 
Trematopora corticosa, Hall. Twenty-sixth Rept. N. Y. State Mus. Nat. Hist-., p. 115. 1874. 
Chcetetes corticosa, Hall. Thirty-second Rept. N. A’. State Mus. Nat. Hist., p. 149. 1880. 
Trematopora ( Clmtetes) corticosa, Hall. Report of State Geologist for 1S82. Expl. pi. 10, figs. 1-10 ; pi. 
13, fig. 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 
