288 Systematic Paleontology 



Description. — This species is closely allied to the associated 0. rhom- 

 lifera but differs in having a considerably smaller zoarium with the 

 zooecial apertures arranged in well-marked, longitudinal rows. The 

 apertures are elongate, oval, .15 to .18 mm. in length, with 15 in the space 

 of 5 mm. ; 10 to 12 rows occur on a branch, separated by prominent ridges, 

 which in old specimens are frequently wider than the cell apertures and 

 often obscure them. 



Occurrence. — Helderbeeg Formation, New Scotland ]\rEMBER. 

 Corriganville. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



Orthopora ovatipora (Hall) 

 Plate L, Pigs. lG-18 



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



figs. 9-11. 

 Trematopora (Orthopora) ovatipora Hall and Simpson, 1887, Pal. N. Y., vol. 



vi, p. 17, pi. xi, figs. 9-11; pi. xxiii, fig. 5. 



Description. — Zoarium solid, ramose, very slender, branches seldom 

 exceeding .15 mm. in diameter. Zooecial apertures arranged in longi- 

 tudinal, parallel rows. Margins of apertures slightly elevated and granu- 

 lose, with a minute spine at each posterior margin. 4 to 5 apertures in 2 

 mm. measuring longitudinally. 



This neat little form may be distinguished from the associated 0. regu- 

 laris by its larger ovate apertures and the smaller number of rows to a 

 branch. 



Occurrence. — Helderbeeg Formation, New Scotland Member. 

 North foot of Moore Knob, Washington County. 



Collection. — U. S. National Museum. 



Family PTILODICTYONIDAE 



Genus PTILODICTYA Lonsdale 



Ptilodictya tenella n. sp. 

 Plate XLII, Fig. 10 ; Plate XLVIII, Figs. 7, 8 

 Description. — Zoarium a simple, unbranched, straight, narrow, bifoliate 

 frond without monticles, 20 mm. or more in length and about 2 mm. 



