30 PKOCEEDINGS OF THE NATIONAL MUSEUM vol.87 



Genus CLONOPORA Hall, 1881 



Zoarium ramose, branches cylindrical, consisting of elongate tubular 

 zooecia cohering for part of their length then bending outward and 

 becoming free; apertures terminal, not contracted, arranged in rings 

 or spirally around the branch (fig. 14, F). 



Genotype. — C. semireduda Hall, 1881 . Lower and Middle Devonian. 



Genus CYSTOPORA Hall, 1881 



Zoarium cylindrical, ramose, consisting of tubular flask-shaped 

 zooecia cohering for the greater part of their length; distally the 

 zooecia bend outward becoming free and much contracted; apertures 

 transversely elliptical, subterminal (fig. 14, G). 



Genotype. — C. geniculata Hall, 1881. Lower and Middle Devonian. 



DESCRIPTIONS OF SPECIES 

 Genus HEDERELLA Hall, 1881 



Hederella Hall, Trans. Albany Inst., vol. 10, p. 194, 1883 (abstract, p. 194, 

 1881). — Hall and Simpson, Pal. New York, vol. 6, p. 26, 1887. — Miller, 

 North Amer. Geol. Pal., p. 308, 1889.— Simpson, 14th Ann. Rep. State 

 Geol. New York, 1894, p. 599, 1897.— Grab au, Bull. Buffalo Soc. Nat. Sci., 

 vol. 6, p. 178, 1899. — Nickles and Bassler, U. S. Geol. Surv. Bull. 173, 

 p. 21, 1900. — Prantl, Acta Mus. Nat. Pragae, vol. 1 (B), p. 75, 1938. 



Nicholsonia Davis (part), Kentucky Foss. Corals, pt. 2, 1885 (name proposed 

 but not defined). [Genotype: A^. canadensis Davis (not Nicholson) = 

 Hernodia davisi and Hederella contortilis, new species.] 



Thamnocoelum Po6ta, Syst. Silur. Boheme, vol. 8, p. 208, 1894. (Genotype: 

 T. fruticosum Po6ta, 1894.) Silurian of Bohemia (see pi. 12, fig. 2). 



This widespread genus is so prolific in species that it is convenient 

 to subdivide it into four groups: (1) The Hederella canadensis group, 

 which includes the numerous species with small zooecia and the 

 rather simple structure of the genotype; (2) the H. alpenensis group, 

 in which the branches divide frequently and the zooecia bud regu- 

 larly and alternately; (3) a group characterized by H. magna, where 

 the tubes, although large, are comparatively short and rapidly expand- 

 ing with wide-open apertures; and (4) the H. parallela group wherein 

 the zooecia remain so long in contact as to appear parallel. In each 

 of these groups the branching and budding and size of tubes are 

 fairly constant in the initial and mature stages, but old examples 

 often develop such a dense network around the oldest part of the 

 zoarium that the real specific characters can be seen only in the 

 younger portions of the colony. Bohemian species of this genus not 

 considered in the present article are H. fruticosa (PoCta) 1894, H. 

 formosa Prantl, 1938, and H. obscura Prantl, 1938. 



