CORALS AND BRYOZOA. 99 



PHRACTOPORA, Hall. 1881. 

 Phractopora cristata. 



PLATE XXXI, FIGS. 36, 37. 



Phractopora cristata. Hail. Trans. Albany Institute, voL x, abstract, p. 12. 18S1. 



Report of State Geologist for 1885. Expl. pi. 31, figs. 36, 37. 1887. 



ZoARiUM consisting of explanate fronds, celluliferous on one or both faces, 

 free or incrusting other objects. The surface is raised at irregular intervals 

 into elevated crests, which are celluliferous on each face, sometimes attaining 

 a height of 5 mm. or more. Cells tubular, arising from a mesotheca, oblique 

 to the surface ; septa wanting. Apertures sub-circular, oblique, diameter .30 

 mm. ; closely dispo.sed, usually in diagonally intersecting rows. Peristomes 

 thin, posterior portion strongly elevated, projecting over and constricting 

 the opening. The maculae consist of circular spaces, 1 mm. in diameter, 

 destitute of cell apertures, and occurring at intervals of about 4 mm. The 

 apertures .adjacent to these do not radiate from them. Intercellular struc- 

 ture, near the base, irregularly vesiculose, becoming regularly septate above. 

 On a portion of one frond the cell apertures are smaller, crescentic, <and 

 denticulated, presenting a very different appearance from the ordinary 

 condition. 



Formation and locality. Upper Helderberg group. Falls of the Ohio river. 

 Phractopora cristata, var. lineata. 



PLATE XXXI, FIGS. »J, 36. 

 Phraclcpora cristata, var. liiteaia. Report of State Geologist for 1885. Expl. pi. 31, figs. 34, 35. 1887. 



In this form the crests are not prominent; frequently the surface is traversed 

 by narrow, slightly elevated carinoe. The cell apertures are more nearly cir- 

 cular, less oblique, and the margins more equally elevated than in P. cristata 

 proper. 



Formation and locality. Upper Helderberg group. Falls of the Ohio river. 



f^-j 



