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Cincinnati Society of Natural Jliatory. 



engine turning.' " " Detached plates have a length that is equal to about 

 three times the greatest breadth, and are somewhat cuneiform in outline, 

 the widest end being that which is exposed." The lower side of each 

 plate is provided with a longitudinal furrow. 



L. ehngatus differs chiefly from the type in being sub-cylindrical in- 

 stead of sub-spherical, though the arrangement of the plates is the same. 



In his remarks on the possible position of the genus, the author 

 considers that these fossils cannot be referred to the echinodermata, " on 

 account of the absence of openings, or of any series of plates that might 

 be termed ambulacra." He further says that it seems related in certain 

 character to Pasccolus, itself of an uncertain position, but considered by 

 some a Cystidian, and by others a sponge. 



I propose to show the identity of these two species to a genus of the 

 order Receptaculio/E, belonging to the sponges. 



The genera comprising the order are four, viz : ISCHADITES, Murchi- 

 son, 1839 (Siluria, p. 697); SpHjEROSPONGIA, Pengelly, 1861 (Geologist 

 IV, p. 340); Acanthochonia, Hinde, 1884 (Q. J. G. Soc, No. 160, 

 p. 819); and Recfptaculi 1 i s, Defrance, 1827 (I)ict. Sci. Nat., t. 45, 

 atlas, p. 68). Though now generally referred to the sponges, the order 

 has been frequently placed witli the Foraminifera, but the arguments for 

 and against its position with the sponges must be neglected here, and the 

 student referred to a paper on the subject by Dr. (i. J. Hinde, published 

 in the Quar. Jour, of (Jeol. Soc. of London, Nov., 1884, p. 395 et seq. 



The genus Ischadites was first described by Murchison in 1839, in 

 his " Siluria," p. 697. In the type species the general form varies from 

 ovate to bi-convex or conical ; " some are sub spherical, and others pi ri- 

 form." (Hinde, /. c, 811.) The central zone is eithei bulged out, or 

 the contour is rounded from base to summit. The base may be obtusely 

 conical, flattened or concave. The outer surface has a number of plates, 

 thickest in the central portion, but diminishing toward the margins, where 

 they are very thin. They are generally rhomboidal. "The manner," 

 says Dr. Hinde (/. c, p. 812) "in which the spicular plates are arranged 

 on the surface of the organism forms its most conspicious feature. They 

 are disposed in regular spiral curves which, starting in opposite directions, 

 from the basal nucleus, and extending to the summit, give to the surface 

 the exact appearance of the engine turned case of a watch." "As a rule, 

 the margins of the plates appear to fit closely and evenly to each other, 

 * * * * * but i n some cases the upper or front margins seem to be 

 slightly elevated, as if they imbricated over the lower Or hind margins of 

 the spicular plates immediately in front." 



