Maryland Geological Survey 287 



Trematopora rhombifera Hall, 1879, Thirty-second Ann. Rept. N. Y. State 



Mus., p. 152 (reprint, 1880, p. 14). 

 Trematopora rhombifera Hall, 1883, Rept. State Geologist N. Y. for 1882-1883, 



pi. xi, figs. 15-20 (not pi. xxiv, figs. 3, 4). 

 Trematopora (Orthopora) rhombifera Hall and Simpson, 1887, Nat. Hist. 



N. Y., Pal., vol. vi, p. 18, pi. xi, figs. 15, 17-20; pi. xxiii, figs. 11, 12 (not 



pi. XXV, fig. 29; pi. xxvi, figs. 3, 4). 



Description. — Zoaritim ramose, apparently dividing at ratlicr frequent 

 intervals; branches .7 to 1.0 mm. in thickness. Zooecial apertures oval, 

 set into rhomboidal or hexagonal sloping vestibular areas, arranged in 

 diagonally intersecting lines, measuring lengthwise 6 to 7 in 2 mm. and 

 diagonally about G in 1 mm. Interapertural spaces ridge-shaped, granu- 

 losa when perfect; a depression occasionally between the ends of the 

 zocecia bordered on each side by two or three small acanthopores. 



In tangential sections taken Just beneath the surface, the zocecia are 

 regularly ovate, enclosed by a dark line and separated by a distance quite 

 as great as their longer diameter ; the interspaces are occupied by strong 

 acanthopores, about four to each zocecium. In a deeper tangential sec- 

 tion, the zocecia are comparatively thin-walled and angular, while the walls 

 show no trace of acanthopores. 



In a vertical section, the zooecial tubes appear to rise from a median line 

 from which they curve outward in all directions. Just before passing into 

 the thick-walled peripheral region in which the acanthopores show dis- 

 tinctly, two large hemi septa are developed. 



The specimens above described agree very well in their internal ap- 

 pearance with 0. rhombifera Hall of the New Scotland beds of New York, 

 but their reference to that species must be considered only provisional 

 since the internal characters of Hall's species are not yet known. 



Occurrence. — Helderberg Formation, Coeymans Member. Cash 

 Valley, Maryland; Keyser, West Virginia. 



Collection. — U. S. National Museum. 



Orthopora regularis (Hall) 

 Plate LI, Figs. 15-17 



Trematopora regularis Hall, 1883, Rept. State Geol. N. Y. for 1882, pi. xi, 



figs. 1-8; pi. xiii, figs. 1-3 (in part). 

 Trematopora {Orthopora) regularis Hall and Simpson, 1887, Pal. N. Y., vol. 



vi, p. 16, pi. xi, figs. 1-8; pi. xxiii, fig. 1. 



