608 GEOLOGICAL SURVEY OF IOWA. 



Actiiiocrinus pernodosus ( n. s.). 



PLATE XV. FIG. 3 a, b; and PLATE XVI. FIG. 7? 



BODY urnshaped, regularly spreading to the base of the 

 arms : dome strongly arched, with a subcentral proboscis ; 

 base deeply excavate for the reception of the column. Basal 

 plates extended at the margins in a strong rim over the 

 column, spreading a little from the inside, and curving in- 

 wards from the outside : a broad and deep indentation ex- 

 tends half the length of the plates, and marks the suture 

 line. First radial plates very large and strong, joining the 

 basal plates by prominent subangular processes. Second ra- 

 dials hexagonal, very strong. Third radials short, pentagonal, 

 supporting on each upper oblique side a pentagonal supra- 

 radial plate, each of which supports a brachial plate on its 

 outer upper side and a second and third supraradial on its 

 inner upper side, the last of which is pentagonal, giving 

 origin to two brachial plates and two arms ; giving six arms 

 to one of the antero-lateral rays : the others unknown. 



First interradial plate hexagonal. Second interradials two, 

 smaller and of the same form, supporting three smaller 

 plates. First anal plate smaller than the first radial : second 

 anal plates hexagonal, supporting a range of four smaller 

 plates ; and these, a second range of four plates. The first 

 and second ranges of each series of plates above the base 

 are very strongly tuberculiform ; the radial plates being 

 somewhat transverse, with sometimes a depression upon the 

 upper side, the other plates having the form of strong tu* 

 bercles. Arm-bases prominent. Dome composed of numerous 

 tuberculiform plates : plates at the base of the proboscis 

 subangularly nodulose. 



This species may be distinguished by its extremely nodose or tuberculiform 

 character of plates of the body. 



Fig. 3 a. Base of the specimen, the posterior side being uppermost. The right postero- 

 lateral ray has the arm-bases broken off close to the body, which gives a 

 somewhat unequal appearance to the two sides. 



Fig. 3 b. Anterior view of same, showing the summit of the third radial plate, 



