360 PALAEONTOLOGY OF ILLINOIS- 



do., to the extremities of the rays, 3.10 inches ; diameter 

 of the opening of the vault, 0.10. 



This species will be readily distinguished from the other known 

 species of the section of the genus with a simple opening in the vault, 

 by its more expanded disc, greater number of arms, and some of the 

 details of its structure, as well as by the sculpturing of its plates. 



Locality and position Upper bed of the Burlington division of the 

 Lower Carboniferous series, at Burlington, Iowa. No. 47 of Mr. 

 WACHSMUTH'S collection. 



STKOTOCKINUS UMBROSUS, Hall (sp). 



PI. 8, fig. 5. 



Actinocrinus umbrosug, HALL. Geol. Report, Iowa, Vol. I, part ii, p. 590, pi. xi, fig. 3 a, b, 1858. 

 Strotocrinus umbrosus, MEEK and WORTHKX. Illinois Geol. Report, Vol. II, p. 190, 1&66. 



BODY urn-shaped, being truiicato-obconic below the arm- 

 bases, and depressed convex above ; sides expanding gradu- 

 ally from the base to a point a little above the third radials, 

 then flaring out abruptly above. Base rather broadly trun- 

 cated below, about three times as wide as high ; basal pieces 

 thick, and separated by such deeply furrowed sutures as to 

 present a trilobate appearance ; facet for the attachment of 

 the column a little less than half the greatest breadth of 

 the column. First radial pieces generally a little wider 

 than long, and presenting the usual hexagonal and heptag- 

 onal outline. Second radial pieces about half as large as 

 the first, and all normally hexagonal. Third radials of 

 about the same size as the second, and varying from hexag- 

 onal to heptagonal ; each supporting on its superior sloping 

 sides, two secondary radials of nearly its own size ; the 

 latter being axillary pieces, bear on their outer sloping 

 sides a series of two or three brachials, the last one of which 

 gives origin to an arm ; while on their inner sloping sides 

 they each support a tertiary radial, giving origin on one of 

 its sloping sides, to a series of brachial pieces leading to an 

 arm as before, and supporting on the other a quaternary 



