334 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



Besides the large zooecia and numerous mesopores, the tabulation 

 is quite distinctive for this species. In the zooecia proper, three or 

 four diaphragms are inserted in the earliest portion of a tube; then 

 they are practically absent until the close of the mature zone, when 

 a few mesopores are occasionally found. The mesopores, as in other 

 species of the genus, are closely tabulated throughout. 



While the present species is quite different from associated bryo- 

 zoans, it is closely related to a new species occurring in the lowest 

 Trenton strata at Belleville, Canada. Indeed, the two agree in all 

 respects save the occurrence of more numerous mesopores in the 

 Russian form. 



Occurrence. — -Rare in the Jewe limestone (Dl), Baron Toll's estate, 

 Kuckers shale (C2), Reval, and in the Kegel limestone (D2), Kegel, 

 Esthonia. 



Cotypes.—Cait. Nos. 57470 to 57472, U.S.N.M. 



HALLOPORA ELEGANTULA (Hall). 



Text fig. 210. 



Callopora elegantula Hall, Nat. Hist. New York, Pal., vol. 2, 1852, p. 144, pi. 40, 

 figs. la-m. — Ulrich, Joum. Cincinnati Soc. Nat. Hist., vol. 5, 1882, p. 250, 

 pi. 11, figs. 6-66. — Simpson, Fourteenth. Ann. Rep. State Geologist New 

 York for the year 1894, 1897, pi. 18, figs. 1-7.— Bassler, Bull. 292, U. S. Geol. 

 Sui-v., 1906, p. 41, pi. 17, figs. 11-15; pi. 26, fig. 12. 



Callopora nana Nicholson, Ann. and Mag. Nat. Hist., ser. 5, vol. 13, 1884, p. 120. 



In breaking up limestone from the Borkholm formation, several 

 fragments of a large celled Eallopora were found, which, upon study 

 with thin sections, proved to be identical with the wide spread early 

 Silurian species H. elegantula. This species has been described and 

 figured on several occasions, so that I need only point out its diag- 

 nostic features. 



The zoarium is of smooth branching stems 3 to 5 mm. in diameter, 

 with large, rounded, thin-walled zooecial apertures, four to five in 

 2 mm., separated by a variable number of mesopores. The aper- 

 tures are frequently closed by ornamental covers, as shown in figure 

 210/. The characteristic tabulation of both zooecia and mesopores 

 is illustrated in figures 210 d and e, while an ordinary tangential sec- 

 tion through the mature zone is shown in figure 210 c. That the 

 perforated closures become the tabulae of succeeding zooecia is evi- 

 dent from figure 210 a. 



The smooth stems and the large, rounded apertures with numerous 

 mesopores in addition to the internal generic characters, will readily 

 serve to distinguish this species. 



Occurrence. — Abundant in almost all of the early Silurian strata of 

 North America. Hall's types came from the Niagaran (Rochester) 

 shale of New York. In Europe the species is known from the Wen- 

 lock shales of England and in the equivalent strata on the island of 



