696 GEOLOGICAL SURVEY OF IOWA. 



large, somewhat concave, each division a little rounded on 

 its outer margin. Poral pieces from eighteen to twenty-three 

 on each side : ovarian opening nearly round. 



The specimens under this name in Dr. TKOOST'S collection resemble so nearly the 

 young of P. stdratus, that I hesitate as to the propriety of retaining the name; and 

 it will require farther comparison to determine fully the relations and differences of 

 these two species. The specimen figured preserves all the characters of the P. globosus 

 of TROOST. 



Fig. 17. A specimen preserving a part of the column and some fragments of the arms 

 or tentacula. 



Geological formation and locality. In the Kaskaskia limestone : Hardin 

 county, Illinois. 



GENUS AGELACRIXUS (VANUXEM). 

 Agelacrinus kaskaskiensis ( n. s.). 



PLATE XXV. FIG. 18. 



BODY discoid, with an apparently entire apex, from which 

 the rays proceed. Rays six, radiating and curving towards 

 the margin so as to come nearly in contact on the periphery, 

 composed of subcuneiform plates which are crenulate or 

 poriferous at their interlocking edges : intermediate spaces 

 occupied by plates of hexagonal or irregular forms, nearly 

 flat. Surface finely granulate. 



The condition of the specimen is such as not to admit of a full description. The 

 rays or ambulacral areas present in some parts apparently a plain double series of 

 cuneiform plates; and in other parts there appear to be intermediate smaller plates, 

 which are extended into tentaculiform processes. 



Fig. 18. View of the specimen, natural size. 



Geological formation and locality. In the Kaskaskia limestone : Kas- 

 kaskia, Illinois. 



