Dec, 1920] Cystids and Blastoids 63 



Remarks. — The characteristic features of Cydocystoides 

 ornatiis are the subtriangular radial cross section of the sub- 

 marginal plates, with the inner face abruptly vertical, and the 

 upper face crossed radially by 4 to 5 low ribs; the individual 

 plates are much wider tangentially than long radially, and 

 usually are distinctly separated from each other laterally, often 

 from half to three-quarters of a millimeter. 



14. Cydocystoides (?) illinoisensis Miller and Gurley. 



(Plate I, Figs. 17 A, B.) 



Cydocystoides illinoisensis Miller and Gurlev, Bull. Illinois State Mu.s. Nat. 

 Hist.,' 6, 1895, p. 61, PI. 5, Fig. 27. 



The species Cydocystoides illinoisensis was founded on two fragments 

 of the submarginal ring, found in the Orchard Creek shale, on Orchard 

 Creek, near Thebes, in Alexander County, Illinois. These specimens 

 differ in character. In the specimen described first, forming Figure 27 

 on Plate 5 accompanying the original description, (Plate I, Fig. 17A of 

 present paper), 9 plates of the submarginal ring are present. These are 

 nearly square in outline, neither the tangential nor the radial diameter 

 differing far from 2 mm. The exposed surface is much flattened in a 

 direction parallel to the disk, and the radial cross-section is very 

 depressed elliptical, with a vertical diameter of 1 mm. The plates are in 

 close contact laterally. Exterior to the submarginal ring are ntrmerous 

 small naarginal plates arranged in short diagonal rows of 3 or 4 plates. 

 Of these, those nearest the submarginal ring are nearly 1.5 mm. in 

 width, while those nearest the free margin are much smaller. 



In their description of this specimen, Miller and Gurley state that 

 the nine large plates present appear not to form more than a third of a 

 circle. In my own opinion, hqwever, they form nearly half of the 

 submarginal ring, the latter being somewhat elliptical in form. At least 

 in a more complete specimen, (Plate I, Fig. 17 B) collected at the same 

 locality, in the same shale, and preserved in the Museimi of Illinois 

 State University, exactly 20 plates are indicated either by plates actually 

 present or by the impression left by those that are missing. 



Locality and Horizon. — From the Orchard Creek shale, 

 on Orchard Creek, near Thebes, in Alexander County, Illinois. 

 The type, numbered 6051 A, is preserved in the Walker Museum, 

 at Chicago University. The specimen here figured belongs to 

 the Museum of the University of Illinois. 



Remarks. — The second specimen figured and described by 

 Miller and Gurley under Cydocystoides illinoisensis is regarded 

 as belonging to Cydocystoides ornatus, Savage, described from 

 the same locality and horizon. 



