PALEONTOLOGY OF IOWA. 



697 



GENUS Aiu H i:oc IDARIS ( M<COY) ; 

 ( Ecliinocrinus, AGASSIZ ; Patoeocidaris, DESOR.) 



FIG. 117. 



BODY spheroidal ; interambulacral spaces composed of 

 three or more rows of plates, those on each side next the 

 ambulacra pentagonal, those of the intermediate ranges 

 hexagonal ; each plate having a central mamillary perforated 

 tubercle, which is surrounded by an elevated ring : to each 

 of these tubercles is attached a large movable spine, which 

 is generally muricate or sometimes spinuliferous, and rarely 

 striate or granulose striate. Surface of the plates marked by 

 radiating ridges, nodes or tubercles. Ambulacral spaces con- 

 sisting of two ranges of alternating poriferous plates. 



From each of the limestones described in the preceding pages, I have selected a 

 single species of ARCHJSOCIDARIS, and grouped them together on Plate xxvi. These 

 are numbered in the order of succession of the rocks, and offer at a single glance 

 characteristic features by which each one may be distinguished. 



With the exception of the Palechinus ( Melonites) multipora of OWEN and NOR- 

 WOOD, I am not aware that any fossils of this family have been described from the 

 Carboniferous limestones below the Coal measures. Dr. SHUMARD, in the catalogue 

 of fossils accompanying the Missouri Report, has enumerated three new species, and 

 [lowA SURVEY.] 88 



