COAL-MEASURE SPECIES 327 



cate, particularly the longitudinal stems and thin branches, all of which 

 are proportionally more slender, so as to form with the dissepiment a 

 finer and more regular reticulated structure. Again, the dimorphous 

 cells of its non-poriferous side are proportionally larger and airranged 

 very regularly on the stems and branches, one at each end of each dissepi- 

 ment, instead of being very irregularly scattered over the whole of the 

 non-poriferous side. If it should be considered desirable to designate this 

 as a distinct variety of S. biserialis, or if it should be found from a careful 

 comparison of a good series of specimens to be specifically distinct from 

 S. biserialis, it may take the name S. gracilis. 



Locality and position : Lower Coal Measures, near Newark, Qhio. 



Genus PTILODICTYA, Lonsdale, 1839. 

 (Murch. Sil. Syst.) 



Ptilodictya (Stictopora) sereata, Meek. 



Plate 20, flg. 4. 



Bifurcating or ramose, the bifurcations occurring usually at rather dis- 

 tant intervals, and the divisions generally diverging at right angles from 

 each other; poriferous surfaces nearly flat or much compressed; lateral 

 margins of both stems and branches sharp and smooth, and provided 

 with very short, obtuse or truncated, alternating, closely and regularly 

 arranged lobes, or flattened lateral divisions, standing out at right angles 

 to the margins, and, like the main stems and branches, bearing pores on 

 each side ; pores small, apparently without distinctly projecting lips, and 

 arranged in quincunx, so as to form on the stems and branches about six 

 to eight longitudinal rows, generally separated from each other in all 

 directions by spaces about equaling twice the diameter of the pores them- 

 selves; surface between the pores smooth or without ridges. 



Entire length of stems and branches unknown ; breadth, exclusive of 

 the short, lateral projections, 0.12 inch ; thickness, about 0.04 inch ; num- 

 ber of pores in 0.10 inch, measaring in the direction of the length of the 

 stems, six ; do., measuring obliquely, about seven. 



This species diflers remarkably from all of the others known to me 

 by the possession of the numerous, very short, regularly and closely 

 arranged, obtuse or truncated lateral divisions, given off at right angles 

 from both lateral margins of stems and branches. At first I was inclined 

 to view these as the remains of lateral branches that had been accident- 



