Trans. Acad. Sci. of St. Louis, 



3. Perischodomus illinoiensis Worthen and Miller. 



1883. Perischodomus Illinoiensis. Worthen and Miller, Geol. 



Surv. 111., vol. 7, p. 333, pi. 31, fig. 8. 

 1889. Perischodomus illinoisensis . Miller, N. Amer. Geol. 



Pal., p. 269. 

 1895. Perischodomus ?f illinoisensis. Keyes, Proc. Iowa 



Acad. Sci., vol. 2, p. 191. 

 1897. Tretechinus illinoiensis . Tornquist, Abhdl. Geol. Karte 



Elsass-Lothringen, Bd. 5, Hft. 6, p. 784. 

 Interambulacra consist of ^yq ? rows of irregular plates, 

 imbricating upward and outward. Ambulacra composed of 

 ^\Q columns of narrow depressed plates overlapped by the in- 

 terambulacral plates. Ambulacral plates pierced by a single 

 pair of pores each, and imbricating slightly from above down- 

 ward. Two kinds of spines present. The central supporting 

 tubercle moderately large, smooth and perforated. Second- 

 ary spine bosses small, conical elevations with a minute per- 

 foration in each. 



Geological formation and locality: Chester Limestone, 

 Bay City, Pope Co., 111. 



INSUFFICIENTLY DETERMINED SPECIES. 



1. Perischodomus magnus Tornquist. 



1893. Perischodomus magnus. Tornquist, Mitth. Geol. Land- 

 esanst., Elsass-Lothr., Bd. 4, Heft. 2, p. 103. 

 Geological formation and locality: Devonian, Ober-Elsass, 

 Germany. 



c. Lepidechinus Hall 1861.* 



General form subspheroidal. Interambulacra consist of 

 from nine to eleven columns of plates imbricating aborally 

 and side wise. Ambulacra consist of two columns of plates 

 imbricating in the opposite direction from those of the inter- 



* Desc. New Species Crinoids, p. 18. 



