BRYOZOA. 571 



theni Hall, and A. terebriformis Ulr., but is not near enough 

 to either to require detailed comparisons. 



Position and locality: Keokuk group, Keokuk, Iowa, Appa- 

 noose (Hall), and three miles northeast of Quincy, 111. 



ARCHIMEDES WORTHEXI Hall. 



PL LXm. Fig. 8-a. 



Archimedes wortheni HalL 1857. Proc. Amer. Ass. Ad. Sci., voL 10, p. 178. 

 Archimedes wortheni Hall, 1858. Pal. Iowa, p. 651, PL XXII, flg. 3, 4a. 4b, 5a, 5b. 

 Archimedes recersa HalL 1858. Ibid. p. 652, PI. XXH, flg. 2. 



Axis large, sub-fusiform, sometimes attaining a length of 

 thirty cm. or more. Volutions regular, dextral and sinistral, 

 varying in different examples from 5 to 6 in 5 cm. Shaft 

 very short, comparatively small, abruptly spreading into the 

 wide flange, the junction between them sharply defined. Upper 

 end of flange flat or slightly concave; lower side usually a very 

 little convex, and uneven, frequently with rather regular verti- 

 cal depressions. Fenestrated expansion as much as six cm. 

 wide, diverging from the axial line at an angle of 65. On the 

 obverse the branches are rigid and closely approximated, the 

 fenestrules appearing very narrow. Separating the two rows of 

 zocecia there is a strong carina, carrying a series of compressed 

 spines. Zooecia about twenty-six in 5 mm., with small, promi- 

 nently elevated apertures, very regularly arranged. On the re- 

 verse the branches are more slender, with from 23 to 25 in 1 

 cm.; the fenestrules are sub-oval, quite as wide as the branches, 

 about once and a half their width in length, and 16 in one cm.; 

 and the dissepiments generally a little stronger than the 

 branches. 



Diam.of shaft, largest ex. 10.0; No. vol. 5 cm., 5.7; diam. fl'ge,28. 

 smallest " 5.1; " " " 6.0; " " 15. 

 average " 7.2; " " " 5.4; " " 20. 



At Bentonsport, Iowa, there occurs what may be a small 

 variety of this species. The length of the axis, as is shown by 

 a nearly complete example, was not much more than 9 cm. 

 There are eight volutions in 5 cm. Another example has only 

 seven in that distance. 



Hall describes A. wortheni, as having occasionally three rows 

 of apertures below a bifurcation, and sometimes with zooecia on 



