CORALS AND BRYOZOA. 73 



The characteristic features of the surface are the longitudinal ridges alter- 

 nating with the rows of nodes. 



Formation and locality. Upper Helderberg group, Onondaga Valley, N. Y. 



ACANTHOCLEMA OVATUM. 



PLATE XXVIII, FIG. 3. 



Treinatcpnra, sp. undt.. Hall. Report of State Geologist for 1882. Expl. pi. 2,5, fig. 3. 1883. 



ZoARiUM ramose, solid ; diameter 1 mm. ; bifurcations infrequent. Cell aper- 

 tures oval, length .22 mm., width one-half the length ; disposed in longi- 

 tudinal parallel rows; twelve rows in the circumference of a branch, separated 

 by narrow, slightly elevated ridges. 



Formation and locality. Upper Helderberg group, Onondaga Valley, Onondaga 

 county, N. Y. 



ACANTHOCLEMA DIVERGENS. 



PLATE XXVUI, FIG. 2. 



Trematoporaf sp. undt.. Hall. Report of SUte Geologist for 1882. Expl. pi. 25, fig. 2. 1883. 



ZoABitiM ramose, solid ; branches .60 mm. in diameter, diverging at an angle 

 of ninety degrees ; bifurcations infrequent. Cell apertures oval, length .24 

 mm., width about one-half the length ; disposed in longitudinal parallel 

 rows; six rows in the circumference of a branch, separated by narrow, 

 slightly elevated ridges. 



This species closely resembles A. triseriale, but the cell apertures are pro- 

 portionally much larger. A critical comparison shows this form to be quite 

 distinct from the preceding {A. ovatum), with which it had been united in the 

 previous descriptions. 



Formation and locaity. Upper Helderberg group, Onondaga Valley, Onondaga 

 county, N. Y. 



