BRYOZOA. 579 



one cm.; the dissepiments one-half as wide as the branches and 

 nearly on a level with them. On the obverse the dissepiments 

 and branches are carinate. the keel with small spines corres- 

 ponding in number with the zooecia, of which there are about 

 22 in five mm. Apertures of moderate size, with slight peris- 

 storne, usually two. sometimes three to each fenestrule. 

 Diaui. of shaft of strongest ex., 1.4 mm.; No. of vol. in 2 cm., 3.5. 



" smallest ik 0.8 " " " " 3.5. 



" average " 1.1 " " " " 3.3. 



This species differs from A. mefikanus Hall, in the longer volu- 

 tions, larger zocecia, and smaller angle of divergence of the 

 feuestrated frond from the axial line. 



Position and locality: Chester group. Not uncommon at 

 Chester. 111. I have also seen several examples from Sloan's 

 Valley, Pulaski Co.. Ky. 



ARCHIMEDES SUBLAXUS Ulrich. 

 PI. Lxm, fig. 14. 



Of this species the specimen figured is the only one seen. It 

 consists of two axes, one sinistral the other dextral, which ob- 

 viously formed part of a single zoarium. The volutions are 

 completed at intervals of 11 or 12 mm., the shaft slender and 

 more or less spiral, from 1 to 1.3 mm. thick, spreading slowly 

 upward into the small flange. Fenestrated expansion 1.5 cm. 

 or less in width, diverging from the axial line at an angle of 

 38 to 40. On the reverse the branches, of which there are 

 22 or 23 in one cm., and dissepiments are rounded, the latter 

 two-thirds as thick as the former: the fenestrules a little longer 

 than wide, as wide as the branches, of subquadrangular form, with 

 about 16 in one cm. On the obverse the fenestrules are a little 

 narrower, and the branches proportionately wider, with an in- 

 conspicuous, faintly spinous keel. Zocecia in two ranges, with 

 small apertures and slightly elevated peristome: about 26 in 

 5 mm. 



The spiral axis of this species is more loosely enrolled and 

 the shaft thinner than in any other of the genus excepting A. 

 laxus Hall. In other respects it resembles the A. owenanus Hall, 

 of the Keokuk limestone. 



Position and locality: Chester group, Chester, 111. 



