BRYOZOA. 669 



This species is closely allied to the S. radialis, of the Keokuk 

 group, but differs in having the longitudinal ridges straighter 

 and nodose, the area oval instead of hexagonal, the mesopores 

 less regularly situated and often placed on the transverse ridges 

 instead of within the area. 



Position and locality: Chester group. Not uncommon at 

 Chester, 111., and Sloan's Valley, Ky. 



STEBLOTRYPA DISTINCT A Ulrich. 



PI. LXXI. flg. 10-106. 



Zoarium consisting of slender dichotomizing stems, from 0.5 

 to 0.7 mm. in diameter. A small slab is almost made up of 

 fragments, from which we may judge the zoarium formed bushy 

 masses. Zooecia apertures generally arranged in longitudinal 

 series, but there are no ridges between the rows. Occasionally 

 a transverse arrangement will predominate, and, more rarely, 

 diagonally intersecting rows are formed. On the whole the arrange- 

 ment is inclined to be irregular. On an average eight occur in 

 2 mm. Apertures oval, 0.10 or 0.11 mm. long, by 0.07 or 0.08 

 mm. wide, with the margin somewhat elevated. Interspaces 

 slightly depressed, varying considerably in width, occupied by 

 more or less numerous, small but unequal mesopores. The in- 

 terspaces between the sides of the peristomes are usually linear. 



The rather irregular arrangement of the zooecia and mesopores, 

 and the absence of longitudinal ridges, give this species a very 

 distinctive and characteristic appearance. 



Position and locality: Chester group. Chester, 111. 



WORTHENOPORA Ulrich. 



(For generic diagnosis see page 403.) 



WORTHENOPORA SPINOSA Ulrich. 



PI. LXVm. Fig. l-lg. 



Zoarium a bilaminar elongate frond, 3 or 4 mm. wide, 0.5 to 

 0.8 mm. in thickness, branching dichotomously or otherwise at 

 long intervals. Acutely elliptical in cross section. Margins sub- 



