362 PALEONTOLOGY OF ILLINOIS. 



Ambulacra linear, comparatively shorter and probably wider than 

 in any other species of Elatacrinus; lancet-piece exposed within the 

 food groove, but only at the upper end of the plate, its lower half 

 is perfectly covered by the side-plates. There are 36 to 38 side 

 pieces, (outer side pieces cannot be distinguished in the specimens) 

 with a deep socket to each plate. The hydrospire-pores are only 

 seen when the side plates are broken away. 



Spiracles ten, one to each side of the ambulacrum; slit-shaped, 

 placed like those of the preceding species within the projecting 

 lateral edges of the orals ; those of the anal side non-confluent with 

 the anal aperture. The hydrospires are unknown. 



The summit (which in both type specimens has been preserved) 

 is composed of but few comparatively thick pieces which are simi- 

 larly arranged as in Elceacrinvs obovatus. Column round, central 

 perforation very small. 



Observations: This species has its closest affinity with Elaacrinus 

 (Nucleocrinus) elegans Conrad, from which it differs in the more 

 elongate form, in the mode of ornamentation, in having almost 

 straight in place of concave interradial sides, and in the less pro- 

 truding and comparatively shorter ambulacra. The latter, in Con- 

 rad's species, reach to the truncate portion of the body, while in 

 E. meloniformis they occupy only five-sixths of that length. It dif- 

 fers from E. Verneuilli in being a much smaller species, and in the 

 entirely different ornamentation ; from Elaeacrinus angular is Lyon, 

 E. lucina Hall and our E. obovatus as lacking that marked angular- 

 ity of the body so conspicuous in each of these species. There is 

 a general resemblance to the figure given by Montgomery of Nucle- 

 ocrinus Canadensis but no direct comparison can be made as his 

 paper deals in generic rather than specific descriptions. The only 

 specific characteristic clearly brought out, "the prominently arched 

 radials" are totally inapplicable to our species. 



Geological position, etc.; In the shales of the Hamilton Group, 

 Buffalo, Iowa, and at the top of the same group in the Thunder 

 Bay region of Northern Michigan. 



