51 



range, above which there are only two in each range or 5x2. 

 In our specimen, in the only regular interradial area in which 

 the plates can be counted, there are eighteen, as follows: One, 

 followed by two in the second range and three in each of the 

 next four ranges, above which three plates may be seen. We 

 have an impression, however, that the number of plates in the 

 interradial areas is not uniform. 



In their species there are from six to seven secondary inter- 

 radials and from three to five tertiary iuterradials. In our 

 species there are from five to seven secondary iuterradials, but 

 no tertiary iuterradials. 



In their species there are six azygous plates in the order of 

 one, two, one, two. In our species the azygous area is larger 

 than the regular interradial areas and has a series of five long 

 longitudinally convex plates, in the middle o1 the area, resting 

 upon. the truncated upper side of a basal plate, and extending 

 as high as the third secondary radial, and, on each side of 

 this ridge of plates there are several smaller polygonal plates, and 

 others extending beyond. There is, therefore, no resemblance 

 between the azygous areas in the two species. 



The radial plates, in both species, as is usual in this genus, 

 are concave on the exterior part of the upper sides and slightly 

 overlapped, in the concave part, by the succeeding plates. 



Their species, therefore, would seem to be more globose than 

 ours, by reason of the wider secondary radials and presence of 

 inter tertiary radials. Our species has more tertiary radials 

 than theirs, differs in the number and position of the regular 

 iuterradials, and is so widely different, in the azygous area, 

 that it alone will distinguisli the species. 



We have uever seen a specimen, which we knew belonged to 

 F. wultihrachiatus, and we suppose it is because their type 

 came from Clear Creek, Hardin County, Kentucky, and there 

 has been error in referring other species to it. 



Found in the Keokuk Group, at Crawfordsville, Indiana, and 

 now in the collection of Wm. F. E. Gurley. 



