CEA THE It. 
SPONGES, GRAPTOLITES AND 
CORALS 
FROM THE 
LOWER SILURIAN OF MINNESOTA. 
BY N. H. WINCHELL AND C. SCHUCHERT. 
Sub-kingdom PORIFERA. 
Order HEX ACTINELLID 4, Schmidt. 
Sub-order LYSSAKINA, Zittel. 
Family RECEPTACULITIDA, Roemer.* 
Dr. Hinde advances the theory that the sixth or summit ray of ordinary hex- 
actinellid sponges has in the Receptaculitide been modified so as to form character- 
istic head-plates. He says (Joc. cit., p. 830), “In no other hexactinellid sponge, so 
far as I am aware, are there any spicules with similarly constituted head-plates ; in 
many, however, no sixth or summit ray is developed, but in some of the abnormal 
spicules of the Carboniferous sponge, Hyalostelia smithiiy Young and Young, sp.. the 
sixth ray is in the form of a rounded knob. We have only to consider that the 
sixth ray in the spicules of the Receptaculitide, instead of heing contracted to a knob 
merely, as in the Carboniferous sponge, has been developed in a horizontal direction, 
and by additions to its margins, has assumed the regular rhomboidal or hexagonal 
*The above systematic position of the Receptaculitidw is that of Dr. George Jennings Hinde. Students desiring to learn 
more of the detailed structure of these species and their affinities to other hexactinellid sponges are referred to Dr. Hinde’s 
admirable monograph “On the Structure and Affinities of the Family of the Receptaculitida, including therein the Genera 
Ischadites, Murchison (Tetragonis, Eichwald); Sphzrospongia, Pengelly ; Acanthoconia, gen. nov., and Receptaculites, 
Defrance,”’ Quar. Jour. Geol. Soc. London, Vol. XL, pp. 795-848. 
In Nicholson and Lydekker’s ‘* Manual of Palwontology ’’, Appendix to Vol. IL, p. 1563, we learn that the Receptaculitide 
have recently formed the subject of an important investigation by Herr Rauft (Zeitschr. d. deutschen geol. Gesellschaft, 
bd.xl). This contribution we are unable to consult. Since, however, Herr Rautf has concluded that * the Receptaculitidw 
are not siliceous organisms. but that the skeleton was originally caleareous, and the siliceous examples are the result of sili- 
fication,” Dr. Nicholson is of the opinion that the family “cannot be referred to the Hexactinellid Sponges,” and that “its 
systematic position is still entirely uncertain.” 
+See Cat. Foss. Sponges, British Museum, pl. 32, fig. 1. 
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