BRYOZOA. 573 



trules once and a half as long as wide, oval or sub-quadrate, 

 about 16 in one cm. Dissepiments rather thick. Obverse not 

 observed. As determined by thin sections, there are about 25 

 zooecia on each side of a branch in five mm. 



The section represented by fig. 2c most probably does not 



belong to this species. It had a much stronger shaft, while the 



angle of the fenestrated expansion, as well as the outline is 



different. In these features it is exactly like the A. intermedius. 



Thick, of shaft of strongest ex. 2.7 mm.; No. of vol. in 2 cm., 9. 



" smallest " 1.0 " 11. 



" average " 2.0 " " " " 10. 



Position and locality: Chester group, Sloan's Valley, Ky., and 

 other localities. 



ARCHIMEDES COMMTTNIS Ulrich. 



PI. LXm, fig. l-ld. 



Axis slender, over twelve cm. in length, approximately of the 

 same diameter throughout; volutions very regular, 7 or 8 in 2 

 cm.; shaft moderately strong, rather deeply and regularly con- 

 cave on each side, so that it is difficult to distinguish the dis- 

 tal from the proximal extremity. Fenestrated expansion nearly 

 always broken away, apparently not over one cm. in width, 

 forming an angle of from 85 to 90 degrees, with the axial line. 

 Branches rounded on the obverse, without a keel, 24 or 25 in 

 one cm.; the zooecia about twenty on each side in five mm., 

 with small apertures and elevated peristome, separated by an 

 interspace equal to once and a half their diameter. Fenestrules 

 elliptical, nearly twice as long as wide, about 15 in one cm. 

 Dissepiments thin. 



Thick, of shaft of strongest ex., 2 mm.; No. of vol. in 2 cm., 8. 

 " " " smallers " 1 " " " 7%. 



" average " 1.3 " " " 8. 



The smaller axis, more regular and numerous volutions dis- 

 tinguish this species from A. swallovanus Hall. In A. inter- 

 medius there are about six volutions in two cm., and the fene- 

 strated expansion forms an angle of 72 with the axial h'ne. 



Position and locality: Chester group. This is the most com- 

 mon as well as the most constant species of the genus. It 



