64 THE PALEONTOLOGY OF MINNESOTA. 



[Ischadites iowensis. 



with Receptaculites, but though similar in its main structural features to this latter 

 genus, it is sufficiently characterized by its conical or ovate form, inclosing a central 

 cavity, with a small summit aperture, and by the absence of an inner layer. From 

 Sphcerospongia, Pengelly, it is distinguished by the rhomboidal form of the spicular 

 plates, and the development of vertical spicular rays ; and from Acanthochonia by its 

 conical ovate form and central cavity." 



Dictyocrinus was at first doubtfully placed among the Crinoidea. Later, however 

 Prof. Hall referred the type species to Receptaculites and then to Ischadites. 



ISCHADITES IOWENSIS Owen, sp. 



PLATE F, FIGS. 5, 6. 



1844. Orbitolites reticulata OWEN. Geological Beport, Iowa, Wisconsin, and Illinois, pi. 18, tig. 7. 

 1852. Selenoides iowensis OWEN. Geological Survey of Wisconsin, Iowa, and Minnesota, p. 587, pi. 



2B, fig. 13. 

 .1861. Receptaculites Selenoides iowene HALL. Report of the Superintendent of the Geological Survey 



of Wisconsin, p. 14. 



1861. Receptaculites fungosum HALL. Ibidem, p. 15. 

 1861. Receptaculites globulare HALL. Ibidem, p. 16. 



1865. Receptaculites iowensis BILLINGS. Palaeozoic Fossils, vol. i. p. 385, fig. 364. 

 1865. Receptaculites iowensis BILLINGS. Canadian Naturalist and Geologist, sec. ser., vol. ii, p. 191, 



tig. 11. 

 V1868. Receptaculites globularis MEEK and WOKTHEN. Geological Survey of Illinois, vol. iii, p. 301, 



pi. 2, flgs. 2a, 2b. 



1868. Receptaculites, sp? MEEK and WORTHEN. Ibidem, p. 301, pi. 2, flgs. la, Ib. 

 1884. Ischadites kcenigii (partim; HINDE. Quar. Jour. Geol. Soc. London, vol. xl, p. 836. 



Original description. " One side flatly dome-shaped, the other ring-shaped, 

 enclosing an umbilicus or centi-al depression. Small rhomboidal cells opening on 

 the surface in curved rows, intersecting in arches ; the cells gradually increasing in 

 size from the inner margin to the periphery." (Owen, 1852.) 



Sponge depressed sub-globose, globose or sub-turbinate ; base more or less con- 

 cave. Greatest width near the base, which varies in diameter from 18 mm. to 70 

 mm. ; bight of the largest and most sub-turbinate form, 35 mm. ; the usual size met 

 with is about 50 mm. in diameter, with a hight of 20 mm. Summit aperture observed 

 in two examples ; one 9 mm., the other 14 mm. in width. This aperture was prob" 

 ably closed by a number of small plates. Head-plates of the spicules not preserved. 

 Spaces formerly occupied by them arranged in spiral curves starting in opposite 

 directions from the nucleus, and extending to the summit. They enlarge as they 

 recede from the nucleus to the zonal region, thence become narrower and more 

 elongated transversely, closely compacted, and constantly diminishing in size towards 

 the summit. The proximal and distal rays of the horizontal rays are usually absent, 

 while the preserved lateral rays give the surface in the upper portion of the internal 

 cast a distinct series of encircling lines. Near the periphery, traces have been 



