PAPERS ON GEOLOGY 265 
In a former paper the Orchard Creek shale was recognized 
as closely allied to the Girardeau limestone, but on account of 
the presence in this fauna of certain species with strong Rich- 
mond aspect, the formation was provisionally referred to late 
Richmond time. More recent study of the fauna of the Gir- 
ardeau limestone and of the Orchard Creek shale, has con- 
vinced the writer that the affinities of the Orchard Creek shale 
fauna are much closer with the Girardeau limestone fauna 
than with that of any Richmond. ‘The large proportion of 
species occurring in both formations may be seen in the above 
list of fossils. The significance of the similarity of the fauna 
of the Orchard Creek shale to that of the Girardeau limestone 
is also much more important than the persistence of a few 
Richmond species in the Orchard Creek beds. Hence the Or- 
chard Creek shale is now considered as representing the in- 
itial deposits in the early Silurian sea that advanced northward 
in this area from the Gulf of Mexico region. 
DESCRIPTION OF NEW SPECIES OF FOSSILS FROM THE THEBES 
SANDSTONE AND ORCHARD CREEK SHALE IN ILLINOIS 
ECHINODERMATA 
CyYSTOIDEA 
Cyclocystoides ornatus n. sp. 
Plate II, Fig. 1. 
Description: In some respects this species resembles Cyc- 
locystoides illinoisensis described by Miller and Gurley from 
the Girardeau limestone, but it may be distinguished from that 
species in having only 20 plates in the submarginal ring (Miller 
and Gurley assume that C. ilinoisensis would have from 24 to 
30 plates), and the upper and outer side of each of these plates 
is marked by 4 transverse grooves while in C. illinotsensis 
there is no indication of such markings. 
In the species here described the submarginal ring is sub- 
circular to subovate in outline, two specimens measured 22 mm. 
in the greater diameter and 19 mm. in the smaller, while a 
q 1. Savage, T. E., Ill. State Geol. Surv. Bull. No. 23. 
