572 PALEONTOLOGY OF ILLINOIS. 



the dissepiments. None of the numerous examples before me 

 exhibit anything of the kind, and I do not doubt that both 

 assertions are based upon defective observation. 



Position and locality: Warsaw beds. 



This is one of the most abundant and characteristic fossils of 

 this horizon. 



ARCHIMEDES PERMINIMUS Ulrich. 



PI. LXIII, Fig. 13 and 11, pars. 



Of this species the example figured is the only one seen. Its 

 axis is, however, so minute in its proportions that I cannot 

 hesitate in pronouncing it distinct from all the other species 

 known to me. In the form and construction the axis reminds 

 us a little of the much larger species A. terebriformis, and it 

 might be urged that A. perminimus is only the terminal or young 

 condition of that species. But such an explanation would not 

 occur to any one who has devoted only a moderate amount of 

 time to the study of these peculiar Bryozoa. The number of 

 volutions in a given space is approximately the same through- 

 out the length of the spiral axis. 



In the specimen under consideration there are four volutions 

 in 5 mm. The shaft of the axis at its thickest part is only 

 0.25 mm. in diameter. The fenestrated expansion must have 

 been very narrow. It is not preserved so as to enable me to 

 give measurements of its minute features. The branches seen 

 bifurcate at each dissepiment, and are about as wide as the 

 fenestrules. The latter are elliptical, with a length equalling 

 about twice the width of a branch. 



Position and locality: Chester group, Chester, 111. 



ARCHIMEDES COMPACTUS Ulrich. 



PI. LXIII, Figs. 2-2e (?2c). 



Axis small, sub-fusiform, not over 6 cm. in length, usually 

 about 3.5 to 4.0 cm.; volutions varying from 9 to 11 in two 

 cm.; shaft comparatively strong, nearly regularly concave on 

 each side. Fenestrated expansion less than one cm. wide, form- 

 ing an angle of 75 with the axial line. Branches slender, about 

 as wide on the reverse as the fenestrules, 24 in one cm. Fenes- 



