XX 



SYNOPSIS OF GENERA. 



both fiices, divided by a inesiiil liiiniua. Margin without cells. Apertures 

 circuhir or 8ub-<iU!ulrate. No intercelluhir tissue, altliough some species show 

 minute interapertural pits or tubuli on the surface of the stipe. 



Examples: Ptilodicli/a tenuis, pi. xvii, figs. 7-12; pi. xxiii a, fig. 15. 

 Plilodidya plumea, pi. Ixi, figs. 9-12. 



Acrogenia, Hall (Trans. Albany Institute, vol. 10, p. 11)3. 1881). 



(Type, Acrogenia prolifera, Hall.] 



Zoriuin ramose, proliferous ; consisting of flattened branches, two proceed- 

 ing from the truncate termination of the previous one, and continuing growth 

 in the same manner. Branches striated below, flattened and celluliferous 

 above. Intercellular structure vesiculose. Apertures arranged in longitudinal 

 rows. 



PLxample : Acrogenia prolifera, pi. Ixiii, figs. 7-15. 



Stictoporina, n. s. g. [Type, Trematopora claviformis. Hall.] 



Zoarium obtusely pointed at the bcase, enlarging above and becoming flat- 

 tened ; bifurcations few. Cells tubular, arising from a mesotheca. Apertures 

 oval. Inter-apertural space elevated, angular, enclosing the apertures in rhom- 

 boidal or polygonal areas. 



Example : Siiciopora {Stictoporina) claviformis, not figured. 



Rhinidictya, Ulrich (Jour. Cinti. Soc. Nat. Hist., vol. v, p. 152. 1882). 

 [Tyjje, Rhinidictya Nicholson!, Ulrich.] 



Zoarium slender, growing as in Stictopora, but with infrequent bifurcations. 

 Cells arranged in alternating longitudinal rows. Peristomes with small gran- 

 ules or spines, which on the interior are continued as tubuli. 



The single species referred to this genus, in the present volume, is of doubt- 

 ful relations, and with equal propriety could be placed under Ptilodictya. 



Example: Rhinidictya? granulosa, pi. xvii, figs. 5, 6; pi. xxiii A, figs. 18, 19. 



Stictopora, Hall (Pal. N. Y., vol. i, p. 73. 1847). 



[Type, Stictopora elegantula, Hall.] 

 Zoarium ramose, growing from an expanded base which is continuous with 

 the frond. Branches flattened, composed of two layers of cells separated by a 

 mesotheca; margins non-celluliferous. Cells tubular, separated by vesiculose 

 tissue. 



