76 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



Genus CERAMOPORA Hall. 



Ceramopora Hall, Amer. Journ. Sci., ser. 2, vol. 11, 1851, p. 400; Nat, Hist. 

 New York, Pal., vol. 2, 1852, p. 168.— Pictet, Traite de Pal., vol. 4, 1857. 

 p. 170. — EicHWALD, Lethsea Rossica, vol. 1, 1860, p. 412. — Zittel, Hand- 

 buch d. Pal., 1880, p. 617.— Vine, Quart. Journ. Geol. Soc. London, vol. 36, 

 1880, p. 358.— Ulrich, Journ. Cincinnati Soc. Nat. Hist., vol. 5, 1882, p. 

 156.— Foeeste, Bull. Sci. Lab. Denison Univ., vol. 2, 1887, p. 169.— Hall 

 and Simpson, Nat. Hist. New York, Pal., vol. 6, 1887, p. xviii. — James and 

 James, Journ. Cincinnati Soc. Nat. Hist., vol. 11, 1888, p. 36. — ^]\Iillek, 

 Nortb Amer. Geol. and Pal., 1889, p. 296. — Ulrich, Geol. Surv. Illinois, 

 vol. 8, 1890, pp. 380, 462.— Pocta, Syst. Sil. Centre Boheme, vol. 8, pt. 1, 

 1894, p. 112.— Ulrich, Zittel's Textbook of Paleontology (Eng. ed.), 1896, p. 

 267. — Simpson, Fourteenth Ann. Rep. State Geologist New York for the year 

 1894, 1897, p. 563.— NiCKLES and Bassler, Bull. 173, U. S. Geol. Surv., 

 1900, p. 23.— Bassler, Bull. 292, U. S. Geol. Surv., 1906, p. 18.— Hennig, 

 Archiv. fur Zool., vol. 4, No. 21, 1908, p. 1. 



ThiS; the typical genus of the family, is sparsely represented in 

 American deposits, where, however, all the vaUd species so far 

 described occur in the Silurian. The discovery of several undoubted 

 forms in the Russian Ordovician is, however, only in line with what 

 would be expected of the geological distribution of the genus. A 

 number of genera were represented in the species originally assigned 

 to Ceramopora by Hall and others, but in 1890 Ulrich ^ restricted 

 the genus to the type species 0. imhricata, making its discoidal growth, 

 peculiar spongy basal tissue in connection with the indefinite wall 

 structure, large mural openings, and absence of diaphragms, the 

 characteristic features. Since that time additional species have 

 been discovered so that at present growth in the genus may be free, 

 discoid, lamellate, massive, or incrusting, the basal spongy layer may 

 be absent and diaphragms may or may not occur. In addition to 

 the ceramoporoid structure, the diagnostic features of the genus are, 

 externally, the occurrence of large, irregular zooecia, comparatively 

 large and equally irregular open mesopores, prominent but often 

 poorly defined lunaria, and, internally, the presence of especially 

 large openings in the walls, allowing communication between the cells. 

 While this delimitation of the genus seems rather indefinite when 

 compared with more sharply defined genera in the family, the very 

 irregularity of the lunarium, zocecium, and mesopores, gives such an 

 unusual aspect to a zoarium that species may be determined with- 

 out much trouble. Indeed, the recognition of a species of Ceramopora 

 is a matter more readily performed by a study of actual specimens 

 than by its description. 



Genotype. — Ceramopora imbricata Hall. Niagaran of the United 

 States and Canada. 



1 Geol. Surv. lUinois, vol. 8, pp. 380, 462. 



