PALAEONTOLOGY OF IOWA. 613 



The peculiar form of this species, and its strongly ridged and spreading arm-bases, 

 aredistinguishingfeatures.lt has sometimes been referred toJl.humboldti of TROOST, 

 but a comparison with the original of that species shows the two to be quite distinct. 

 A. humboldti is remarkable for its large basal plates and large first radials, the height 

 of the body to the top of the second radial plate being greater than the entire height 

 of the body of the present species. 

 Fig. 5 a. Anal side of specimen. 



Fig. 5 b. View of right antero-lateral side, the arm-base of which is smaller than the 

 others. The cavity near the summit is only from the breaking away of some 

 of the plates, and is not an organic feature. 



Geological formation and locality. In Keokuk limestone near Warsaw, 

 Illinois. 



Actinocrimis gouldi ( n. s.). 



PLATE XV. FIG. 6 a, b. 



BODY urnshaped, convex above, and marked by a long 

 central slightly curved spine and five superior lateral spines : 

 base large, deeply excavated. Basal plates spreading and 

 almost recurved at their lower margins, deeply and broadly 

 grooved at the suture lines. First radial plates nearly twice 

 as wide as long, transversely and strongly ridged. Second 

 radials quadrangular, wider than long. Third radials penta- 

 gonal or heptagonal, supporting on each upper oblique side 

 a pentagonal supraradial plate, which sustains on each upper 

 side two brachial plates in succession, or a first and second 

 supraradial ; the last supporting on one sloping side two 

 brachial plates, and on the other a single plate. First inter- 

 radials heptagonal or octagonal : second series consisting of 

 two oblique heptagonal plates, which support a narrow cen- 

 tral hexagonal plate and two small subpentagonal plates. 

 First anal plate a little larger than the first radial plates, 

 succeeded by three other plates. The dome, above each set 

 of arms, and separated from them by two intervening ranges 

 of plates, supports a long and somewhat curving spine, which 

 is usually marked in some part of its length, or almost 

 entirely, by small spiniform nodes : within the bases of 

 these five spines are two ranges of plates, the inner one 

 surrounding and supporting a strong central spine, which is 



