670 PALAEONTOLOGY OF ILLINOIS. 



parallel, armed with a series of slender spines from 0.3 to 0.5 

 mm. long, pointing obliquely upward and outward. There are 

 on each side about sixteen in 3 mm. Zooecia enclosed by an 

 elevated sub-a,ngular ridge, common to adjoining zooecia. The 

 space enclosed is elongate, somewhat rhombic in shape, drawn 

 out long wedge-shaped posteriorly, and more rounded anter- 

 iorly; the whole usually 0.6 mm. long and 0.12 mm wide. 

 Aperture semi-elliptical, truncated posteriorly, 0.18 mm. long, 

 and 0.1 mm. wide, occupying the anterior third of the space 

 enclosed by the ridges, which form its margin except at the pos- 

 terior side, where a thinner and less elevated line separates the 

 aperture from the remainder of the enclosure. The latter forms 

 an irregular sub-triangular depressed space, with the bottom 

 smooth and slightly concave. When perfect five small tuber- 

 cles, one on the posterior and two on each of the lateral mar- 

 gins, project into the aperture. Apertures arranged in regular, 

 acutely intersecting, diagonal series, nine in 3 mm., and in less 

 regular transverse rows, between eight and nine in 2 mm. The 

 marginal rows of zooecia are usually a little larger than the 

 central ones. 



Position and locality: Keokuk group. Warsaw and Nauvoo, 

 111.; Keokuk and Bentonsport, Iowa; Warsaw beds, at War- 

 saw, 111. 



WORTHENOPORA SPATULATA Prout. 



PI. LXVIII figs. a-2a. 

 Flustra spatulata Prout, 1859. Trans. St. Louis Acad. Sci. vol 1. p. 446. PI. 17, fig. 2-2c. 



This species differs from W. spinosa mainly in the form of 

 the zoarium which is always more explanate, being usually of 

 flabellate form. The margins are sharp and striate, and with- 

 out spines. On one fragment many of the triangular suboral 

 spaces are divided in half by a thin transverse ridge. 



Position and locality: Warsaw beds, Warsaw, 111., and Bar- 

 rett's Station, St. Louis county, Mo. 



