224 BULLETIN 77, UNITED STATES NATIONAL, MUSEUM. 



single cluster or macula will distinguish tlie species from other Stelli- 

 foras and also other Russian bryozoans save Scenellopora socialis 

 (Eichwald). The zooecia of the latter are so different in shape and 

 arrangement that no confusion should arise. Of American forms, 

 the one nearest to S. apsendesoides is a new species or variety from 

 the Black River shales of Minnesota, having the same method of 

 growth and differing only in its smaller zoarium with fewer and less 

 sharply raised rays. 



Occurrence. — Rare in the Echinospherites hmestone (Cl) at the 

 Red Light House, Reval, Esthonia. 



Holotype.— Cat. No. 57304, U.S.N.M. 



Genus NICHOLSONELLA Ulrieh. 



Nicholsonella Ulrich, Geol. Surv. Illinois, vol. 8, 1890, pp. 374, 421; Geol. and 

 Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 1893, p. 313; Zittel's Textbook 

 of Paleontology (Eng. ed.), 1896, p. 276. — Simpson, Fourteenth. Ann. Rep. 

 State Geologist of New York for the year 1894, 1897, p. 590.— Nickles and 

 Bassler, Bull. 173, U. S. Geol. Surv., 1900, p. 34.— Bassler, Bull. 292, 

 U. S. Geol. Siu-v., 1906, p. 37. — Cumings, Thirty-second Ann. Rep. Dep. 

 Geol. Nat. Res. Indiana, 1907, p. 751. 



Species of NicJiohonella are readily recognized in thin sections 

 by the presence of a granular, calcareous deposit in the outer part 

 of the mature zone, filling the interzooecial spaces and obscuring 

 the walls of the mesopores. The walls of both zooecia and meso- 

 pores are traversed longitudinally by minute tubuli, which, in 

 tangential sections and at the surface appear as granular, acantho- 

 pore-like structures. Somewhat similar granular structures are 

 present in Constellaria with which Nicholsonella is beheved to be 

 alUed, although the absence of such distinct, star-shaped maculae 

 in the latter is an easy means of separation. The following well 

 marked species has characters quite different from any known 

 American form of NicJiohonella but there seems to be no reason 

 for not referring it to the genus. 



Genotype. — Nicholsonella ponderosa Ulrich. Middle Ordovician 

 (Black River) of Illinois and Minnesota. 



NICHOLSONELLA GEBBOSA, new species. 

 Plate 11, figs. 1-6; text figs. 125, 126. 



Cfr. Heteropora gibbosa Eichwald, Lethsea Rossica, vol. 1, 1860, p. 419, pi. 26, 

 figs. 6 a, b. 



Zoarium of small masses varying in shape from regular hemi- 

 spheric forms with a flat or slightly concave concentrically wrinkled 

 base, to irregular, elongated or nodulated lumps. The regular 

 hemispheric zoaria occur most often and are usually about 15 mm. 

 in diameter and 6 or 7 mm. high. Continued growth in one direction 

 gives rise to forms several centimeters long and a centimeter or 



