50 AMEBIC AN FOSSIL BRYOZOA. [bull. 173. 



expansions or triangular branches; zooecia semicordate or obovate- 

 acuminate in outline, arranged longitudinally; orifices subcircuiar, 

 vestibule elongated; apertures with peristome and more or less well- 

 developed lunarium; interzooecial spaces occupied by vesicular tissue, 

 often tilled with a calcareous deposit near the surface, 



Cystodictta Ulrich (Arcanopora Vine, Stictocella Simpson). 



Zoarium ramose, branches sharply elliptical in cross section, with 

 subparallel, nonporiferous margins; apertures subelliptical, in linear 

 series between longitudinal ridges, which may not always be present, 

 lunarium on the side of the aperture nearest the margin of the branch; 

 interspaces finely striated, granulose or smooth; pits and cells show 

 onh" in a worn condition. 



Genotype: Cystodictya ocellata Ulrich. Range, Devonian-Carbon- 

 iferous. Thirty -five species. 



DiCHOTRYPA LTlrich. 



Zoarium a large, thin, bifoliate expansion; surface with solid macu- 

 Ise; otherwise as in Cystodictya. 



Genotype: Dichotryjxi foliata Ulrich. Devonian, Mississippian. 

 Seven species. 



CosciNiUM Keyserling (Coscinotrypa Hall and Simpson). 



Zoarium of flattened branches, celluliferous on both sides, which 

 inosculate at short intervals till there is produced a broad frond, per- 

 forated at rythmical intervals by circular or elliptical fenestrules; in 

 other respects like Cystodictya. 



Genotype: Cosciniwn cy clops Keyserling. Range, Devonian-Car- 

 boniferous. Five species. 



TiENiopoRA Nicholson (Pteropora Hall, Stictoporidra Simpson). 



/Zoarium with a strongly elevated longitudinal central ridge on each 

 face, so that a cross section of the branches is somewhat rhomboidal; 

 otherwise like Cystodictya. 



Genotype: Tmniopora exigua Nicholson. Devonian. Five species. 



Thamnotrypa Hall (Thamnopora Hall). 



Zoarium consisting of a very narrow stipe, from which proceed rectangularly lat- 

 eral branches; celluliferous on each face; cell apertures oval; usually disposed in 

 two parallel longitudinal rows, separated by a prominent ridge. Sometimes three 

 rows occur and occasionally four rows for a short distance on the stipe. On the lat- 

 eral branches there are nevermore than two rows.' 



Genotype and only known species: Thamnopora divaricata Hall. 

 Devonian. 



1 Simpson, Fourteenth Ann. Rep. State Geologist New York for tlie year 1894, p. 546. 



