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 
Spherospongia, 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 Receptuculites and then to Ischadites. 
ISCHADITES LOWENSIS Owen, sp. 
PLATE F, FIGS. 5, 6. 
1844. Orbitolites reticulata OWEN. Geological Report, Iowa, Wisconsin, and Illinois, pl. 18, fig. 7. 
1852. Selenoides iowensis OWEN. Geological Survey of Wisconsin, Iowa, and Minnesota, p. 587, pl. 
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. eceptaculites globulure HALL. Ibidem, p. 16. 
1865. Receptaculites iowensis BILLINGS. Paleozoic Fossils, vol, i. p. 385, fig. 364. 
1865. Receptaculites iowensis BILLINGS. Canadian Naturalist and Geologist, sec. ser., vol. ii, p. 191, 
fig. 11. 
?1868. Receptaculites globularis MEEK and WORTHEN. Geological Survey of Illinois, vol. iii, p. 301, 
pl. 2, figs. 2a, 2b. 
1868. Receptaculites, sp? MEEK and WORTHEN. Ibidem, p. 301, pl. 2, figs. la, 1b. 
1884. Ischadites keenigii (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 central 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.; hight 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 20mm. 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 
