700 GEOLOGICAL SURVEY OF IOWA. 



Fig. 3 a. A fragment, natural size, showing several plates and a small group of the 

 spines. The figure is a part of a much larger mass of plates and spines. 

 Fig. 3 b. A single plate enlarged. , 



Fig. 3 c. Profile view of the same. 



Fig. 3 d. A single spine twice enlarged. The accompanying figures are a section of 

 the spine, and enlargements of the surface markings on the middle and 

 . lower parts. 



Geological formation and locality. In the Warsaw limestone : Warsaw, 

 Illinois. 



Arclueocidaris wortlieni (n.s.). 



PLATE XXVI. FIG. 4 a - g. 



BODY spheroidal, the central upper portion composed of 

 numerous small imbricating plates. Interambulacral spaces 

 composed of four ranges of plates, the two inner ones hexa- 

 gonal, the others pentagonal, with a convex side adjoining 

 the ambulacral areas. Central tubercle papilliform, mode- 

 rately elevated above the annulation, the space between it 

 and the annulation slightly concave : annulation thickened 

 and spreading below into a slightly elevated disc, between 

 which and the denticulate margin the surface is nearly flat. 

 Plates of the ambulacral areas in a double alternating series, 

 wide and short, pentagonal, interlocking at their obtusely 

 wedgeform margins ; each plate with two oval pores. Spines 

 slender, elongate, slightly curving, smooth or finely granu- 

 late ; articulating extremity expanding from above into a 

 crenulate annulation, and abruptly contracting below. 



This species, in the form of its smooth spines, is remarkably distinct from the 

 others described; the plates are in form and proportions similar to the Warsaw 

 species, but larger and less concave, as well as less strongly nodose on the margins. 



The specimens under examination show the body nearly entire, and almost com- 

 pletely flattened. From other fragments it would appear that the body, in its natural 

 condition, was very depressed spheroidal, with the sides broadly rounded and base 

 a little concave. 



Fig. 4 a. Upper side of a crushed specimen. The small imbricating plates of the summit 



are not well shown in the figure. 

 Fig. 4 b. Base of specimen, showing the displaced and crushed plates, with several broken 



spines. 

 Fig. 4 c. A single plate enlarged, showing the mamillary tubercle, the annulation and 



surrounding disc, etc. 

 Fig. 4 d. Profile of the same. 



