SPONGES, GRAPTOLITES, CORALS. 



65 



Ischadiles. ] 



observed of one of the horizontal rays of a spicule extending beyond the distal 

 angle of its summit-plate over that of the one immediately in front. Vertical rays 

 of spicules subcylindrical, about 15 mm. in length. 



The above synonomy and Receptaculites ohioensis Hall and Whitfield, R. sub- 

 turbinatus Hall, and R.jonesi Billings, Dr. Hinde regards as embracing but a single 

 species, Ischadites kienigii Murchison. R. ohioensis and R. subturbinatus are from the 

 Niagara group of Ohio and Indiana ; the first differs in the comparatively large head- 

 plates and in its strongly convex base, while the latter has much larger head plates 

 on the sides than Ischadites iowensis. R.jonesi agrees with Ischadites iowensis in form 

 but as it is from a later geological horizon, we prefer to retain the species, partic- 

 ularly since we have no examples for comparison. Ischadites iowensis is constantly 

 more or less strongly concave, never conical, and but rarely flattened on its under side. 

 It attains a larger size and has comparatively smaller head-plates than I. kcenigii. 

 Since these features are constant in I. ioivensis, we deem it sufficient ground to retain 

 this species as distinct from that form. 



All the specimens of I. iowensis from Minnesota, seen by .the writers, are de- 

 pressed sub-globose, never sub-turbinate. I. fungosus Hall might be recognized as a 

 good variety, were it not that both forms have been found lying with the umbilicated 

 side downwards within a foot of each other, in the side of a cliff at Decorah, Iowa. 



Formation and locality. Galena formation of Iowa, Wisconsin, and Minnesota. In Minnesota, this 

 species is usually obtained from the lower portion of the Galena ; some localities are six and twelve miles 

 south of Cannon Falls in Goodhue county, and Wasioja, Dodge county. Mr. F. W. Sardeson informs the 

 writers that he obtained this species in the Hudson River or Cincinnati group, near Spring Valley, 

 Minnesota. 



Mus. Beg. Nos. 5839, 6760, 7250. 



SYNOPSIS OF AMERICAN SPECIES OF ISCHADITES. 



I. CTATHIFOEMIS Hall. 



1847. - cyathtformis HALL. Paleontology of New York, vol. i, p. 72, pi. 25, flg. 6a-6c. 

 Closely related to 1. iowensis. 



Formation anil locality. Trenton limestone ; Carlisle, Pennsylvania. 



I. CIRCULARIS Ernmons. 



1885. Receptaculites circularis EMMONS. American Geology, pt. ii, p. 230, flg. 82. 



1891. Receptaculites circularis JAMES. Jour. Cincinnati Soc. Nat. Hist., vol. xiv, p. 63. 



This species may be identical with /. Iowensis, but the spicular head plates seem to be larger. 



Formation and locality. Loraine shales; New York. 



I. JONESI Billings. 



1865. Receptaculites jonesi BILLINGS. Palaeozoic Fossils, vol. i, p. 389, flg. 365. 



1865. Beixptaculites jonesi BILLINGS. Canadian Naturalist and Geologist, sec. ser. vol. ii, p. 191, flg. 12 

 1884. Ischadites Jcoenigii (partim) HINDE. Quart. Jour. Geol. Soc. London, vol. xl, p. 836. 

 See remarks on this species under I. iowensis. 



Formation ami InratU}/. Lower Helderberg proup ; Cape Gaspe. 

 -R 



