128 



BULLETIN" 11, UNITED STATES NATIONAL MUSEUM. 



STICTOPORELLA CRIBROSA Ulrich. 



Plate 7, fig. 4; text figs. 52, 53. 



Sdctoporella? aibrosa Ulrich, Foui-teenth Ann. Rep. Geol. Nat. Hist. Surv. 

 Minnesota, 1886, p. 69. 



Stictoporella cribrosa Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 

 1893, p. 184, pi. 10, figs. 21-25; pi. 11, figs. 22, 23.— Simpson, Fourteenth 

 Ann. Rep. State Geologist New York for the year 1894, 1897, p. 536, fig. 93. 



Zoarium composed of narrow, bifoliate, smooth branches, aver- 

 aging 2,5 mm. in breadth, Inosculating so frequently that a broad 

 expansion perforated by rounded or elliptical fenestrules at rather 

 irregular intervals is the result. Specimens preserving the basal 





Fig. 52.— Stictoporella ckibrosa. a, nearly complete zoarium natural size; 5 and c, surface of 



A SPECIMEN ■WITH NUMEROUS MESOPORES, X9 AND A POETION XI 8; d, VERTICAL SECTION, X18; C, TAN- 

 GENTIAL SECTION OF AN AVERAGE SPECIMEN, XIS. BLACK RiVER (DeCORAH) SHALES, MINNEAPOLIS 



Minnesota. (After Ulrich.) 



portion are not common, but show clearly that the zoarial growth 

 is from a small incrusting basal expansion mto thin, erect fronds. 

 The largest of the Russian specimens, although still incomplete, is 

 over 70 mm. in its longer diameter. Fronds celluliferous on both 

 sides, as usual in such bifoliate specimens. Fenestrules about 2 mm. 

 in their greatest diameter, although a variation of 1 mm. in each 

 direction from this figure may be observed. This irregularity of 

 the fenestrules is matched by a corresponding variation in the width 

 of the branches, which range from 1.5 mm. to 3 mm., in round 

 numbers. Zooecial apertures small when compared with other 

 bryozoans, but large for this particular section of the genus, subcir- 

 cular and set in well-defined, polygonal, sloping areas. The usual 



