668 PALEONTOLOGY OF ILLINOIS. 



small, almost vertical in the middle of . the axial region, ap- 

 proaching the surface slowly, and increasing in size a.t the same 

 time. Between 0.2 and 0.3 mm. from the aperture a short 

 inferior hemiseptum is developed. Zocecia apertures ovate, 

 slightly truncated posteriorly, 0.08 mm. long by 0.06 mm. 

 wide, surrounded by a thin peristome highest at the anterior 

 border. They are arranged in alternating longitudinal rows 

 between thin ridges which unite with the peristomes and are 

 about 0.1 mm. apart. The interspaces between the succeeding 

 apertures is depressed and occupied by the mouths of from nine 

 to fifteen small pores arranged in two or three rows. Measuring 

 longitudinally six zooecia apertures occur in 2 mm.; diagonally 

 five in 1 mm. It requires about twelve rows to encircle the 

 stem. 



The small zooecia apertures, their regular arrangement, and 

 the large number of the (?) mesopores. are the distinguishing 

 features of this species. 



The specific name is given in honor of Mr. J. M. Nickles, of 

 Sparta, 111., to whom belongs the credit of first finding the 

 species in abundance. 



Position and locality: Chester group. Common at Kaskaskia 

 and other localities in 111., and at Sloan's Valley, Ky. Accord- 

 ing to Mr. Vine (Proc. Yorksh. Geol. Soc., vol. VIII, p. 107, 

 1885,) also in the Carboniferous shales of England. 



STREBLOTRYPA SUBSPINOSA Ulrich. 



PI. LXXI, figs. 7-7a. 



Zoarium consisting of long, slender, cylindrical stems, 0.7 or 

 0.8 mm. in diameter, branching dichotomously at varying in- 

 tervals. Zooecia apertures arranged alternately in longitudinal 

 series, nine or ten in 3 mm.; diagonally five in 1 mm. Between 

 the series are nearly straight longitudinal ridges carrying a 

 variable number of small nodes. Between the ends of the de- 

 pressed apertures, which occupy the bottom of distinct oval 

 sloping areas, there are from two to four small mesopores. 

 These sometimes occupy the transverse ridges, at other times 

 the posterior slope of the area. 



