228 SYSTEMATIC PALEONTOLOGY 



Description. " Zoarium jointed ; segments about 7.0 mm. long, obtuse 

 at both extremities, subcylindrical, polygonal in cross-section, the number 

 of the angles and corresponding rows of zocecial apertures six, seven or 

 eight. Their diameter varies with age and according to the number of 

 zorecia contained from 0.5 to 0.9 mm. Zooacial apertures comparatively 

 large, oblique, ovate, seeming to widen anteriorly, arranged in troughs 

 between strong longitudinal ridges, 12 in 5 mm. lengthwise and generally 

 in regular transverse rows. Posterior border of apertures thick, promi- 

 nent, sloping backward into the aperture next below. This border is 

 continued upon the sides of the zocecial aperture as two diverging ridges 

 which extend on each side to the summit of the longitudinal keels where 

 they meet with similar ridges from the adjoining rows. These divaricat- 

 ing ridges cause the strong vertical keels to appear as being marked by a 

 succession of narrow A-shaped furrows and ridges. Occasionally, and 

 this is true more especially of the young and slender segments, the 

 rounded posterior slope is divided by a central furrow into two small 

 ridges." Ulrich, 1893. 



Occurrence. CHAMBERSBURG LIMESTONE (Caryocystites bed). Fort 

 Loudon, Franklin County, Pennsylvania. This species has heretofore 

 been recorded from the Decorah shales of the Black Eiver group of Minne- 

 sota and the Kuckers shales of Esthonia, Eussia. 



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



HELOPORA SPINIFORMIS (Ulrich) 

 Plate XLIV, Figs. 8-10 



Arthroclema spiniformis Ulrich, 1882, Jour. Cincinnati Soc. Nat. Hist., 



vol. v, p. 161, pi. vi, figs. 10, lOa. 

 Helopora spiniformis Ulrich, 1893, Geol. Minnesota, vol. iii, pi. iii, figs. 4-6. 



Description. " Zoarium composed of numerous segments, which are 

 cylindrical, poriferous on all sides, and pointed more or less obtusely at 

 each end; their length varies from two- to four-tenths of an inch, their 

 diameter from .015 inch to .04 inch. Cell apertures oblique, arranged 

 between slightly elevated longitudinal lines, and in transverse rows 

 around the stem. On account of their obliquity, well-preserved examples 



