XX 
SYNOPSIS OF GENERA. 
both faces, divided by a mesial lamina. Margin without cells. Apertures 
circular or sub-quadrate. No intercellular tissue, although some species show 
minute interapertural pits or tubuli on the surface of the stipe. 
Examples: Ptilodictya tenuis , pi. xvii, figs. 7-12; pi. xxiii a, fig. 15. 
Ptilodictya plumea, pi. Ixi, figs. 9-12. 
Acrogenia, Hall (Trans. Albany Institute, vol. 10, p. 193. 1881). 
[Type, Acrogenia prolifera, Hall.] 
Zorium 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. 
Example: Acrogenia prolifera , pi. lxiii, figs. 7-15. 
Stictoporina, n. s. g. [Type, Trematopora claviformis, Hall.] 
Zoarium obtusely pointed at the base, 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 : Stidopora ( Stictoporina ) claviformis , not figured. 
Rhinidictya, Ulrich (Jour. Cinti. Soc. Nat. Hist., vol. v, p. 152. 1882). 
[Type, Bhinidictya Nicholsoni, 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. 
