350 PALAEONTOLOGY OF ILLINOIS. 



From the same locality and position we have a few specimens of a nearly 

 allied form, that may possibly belong to the same species as this, though we 

 think they are distinct. These are considerably larger and less depressed, 

 with scarcely any traces of radiating markings, but have more distinct concen- 

 tric wrinkles. They also differ in being more broadly rounded in front. 



The species under consideration (#. radiata) seems to be related to S. pri- 

 meeva of Phillips (Gcol. Yorksh., vol. ii, tab. 5, fig. 6), but differs in being less 

 depressed, more narrowly round in front, and entirely destitute of any traces of 

 fine radiating striae between the obscure costse. 



Locality and position: Schuyler county, Illinois; Coal Measures. 



Genus ALLOKISMA, King, 1844. 



(Ann. Mag. Nat. Hist., siv, p. 315.) 



Allorisma (sp. undt). 



PI. 27, fig. 9, 9 a. 



The only specimen of this species we have seen is a mere cast, not entirely 

 perfect at either extremity, so that we have not the means of determining sat- 

 isfactorily whether it is new or not. As near as can be determined, it seems 

 to' be proportionally shorter and more gibbous than any otherwise similar spe- 

 cies with which we are acquainted. In a side view it is not unlike a species 

 from the middle Coal Measures at Lexington, Missouri, described by Prof. 

 Swallow, under the name A. lata. On comparison, however, with the typical 

 specimen of that species, it was found to be much more gibbous, and marked 

 with proportionally larger concentric ridges. Compared with A. subcuneata, 

 Meek and Hayden, from the Coal Measures of Kansas {Paleontology Upper 

 Missouri, pi. i, fig. 10a, 106), it will be seen to be proportionally much shorter, 

 and more broadly rounded posteriorly. 



Locality and position: North Branch Saline creek, Gallatin county, Illinois* 

 Upper Coal Measures. 



