BRYOZOA. 575 



The smaller number of volutions, and the larger and stronger 

 axis, distinguish this species from A. communis and intermedius. 



It has not been found in the Chester group localities of Ken- 

 tucky, where both of these species are abundant. 

 Diam. of shaft of strongest ex. 6.7 mm.; No. of vol. in 2 cm., 5. 



another " 5.0 " ." " 4& 



smallest " 2.8 " " " " 5. 



" average " 4.0 " " " 5. 



Position and locality: Chester group, at Chester and other 

 localities in Illinois. 



ARCHIMEDES TEREBRIFORMIS Ulrich. 



PI. LXm, figs. 5-oc. 



Axis rather slender, just a little fusiform, the largest specimen 

 seen, which appears to be almost complete, is ten cm. long; 

 volutions quite regular, varying in different examples from 3 

 to 4.2 in two cm.: shaft comparatively thin, distinctly spiral, 

 thickened just below the spiral flange, the thickening best shown 

 in medium sized specimens. Fenestrated expansion of unknown 

 dimensions, forming an angle of from 60 to 65 with the axial 

 line. 



This form is readily distinguished from ah 1 the associated 

 species by the spiral form of the shaft, and the swelling just 

 beneath the flange. In other respects it compares closely with 

 A. negligens, from the Keokuk group. The collection before me 

 contains eight axes of what is probably a variety of this spe- 

 cies. They lack the swelling below the flange, and have con- 

 stantly 4.8 to 5 volutions in two cm. So far as observed they 

 do not differ in any other respect from the typical specimens. 

 Diam. of shaft of strongest ex. 2.5 mm.: No. of vol. in 2 cm., 3.1. 

 smallest ; - 1.1 " " " 3. 



average " 2.0 " " " " 3. 



Position and locality: Chester group, Chester, Illinois, and 

 rarely at Sloan's Valley and Grayson Springs, in Kentucky. 



ARCHIMEDES IXVA<;I.\ATUS Ulrich. 



PL LXD3. figs, lla, lie. 



Axis rather strong, usually a little curved, over ten cm. long 

 when complete, diminishing very gradually in strength toward 



