THE NATURAL HISTORY SURVEY. 269 



Eyes small, placed just in front of the bases of the cheek spines, 

 in the rounded angle between the bases of the spines and the 

 base of the globular frontal lobe of the glabella, they are raised 

 on slight prominences which extend obliquely forward. Neither 

 the pygidium nor the thorax have been observed from the 

 Niagaran fauna of the Chicago area. 



The dimensions of a nearly complete cephalon are: length 

 along median line 8 mm., width of frontal lobe of the glabella 

 7.5 mm., width between extremities of cheek spines 19 mm. 



Remarks. The presence of the genus Deiphon in the Ni- 

 agaran fauna from near Batesville, Arkansas, has been noted by 

 van Ingen*, the Arkansas specimens being identified by that 

 author with the European D. forbesi Barr. A species of the 

 genus has also been described and illustrated as Sph&rexochus 

 pisum by Foerstef, from beds of Clinton age in Ohio, the cheek 

 spines not being preserved in the specimen figured, and the 

 presence of the same species in the Niagaran beds of New York 

 is mentioned. These occurrences, with the presence of the 

 same genus in the Chicago area, show that this highly specialized 

 genus had a wide geographic distribution in the North American 

 epicontinental seas of Silurian age. In Europe the species 

 D. forbesi Barr., is reported from England and Bohemia. 



The species which is here described as D. americana differs ' 

 from the European D. forbesi in its broader' occipital furrow 

 with the pit-like depressions at either end, and in the more 

 posterior position of the cheek spines, the bases of these spines 

 being nearly opposite the middle of the globular frontal lobe 

 of the glabella in Bohemian examples as illustrated by BarrandeJ. 

 The Arkansas specimens are probably identical with the Chicago 

 species, while the Ohio specimens described by Fcerste more 

 closely resemble the European D. forbesi. 



Localities. Joliet, Romeo, Chicago Drainage Canal near 

 Lemont. 



Genus 19. STAUROCEPHALUS Barrande, 1846. 



Complete body sub-ovate in outline. Cephalon with a 

 conspicuous globular anterior glabellar lobe produced entirely 

 beyond the frontal margin of the head, the lateral glabellar 

 lobes reduced in size; cheeks of moderate size, convex, with 

 short genal spines; eyes small. Thorax strongly trilobed, 



*School of Mines Quart., Vol. 23, p. 35. 



tGeol. Surv. Ohio, Vol. 7, p. 528, pi. 37A, figs. 14 a-b. 



SSyst. Sil. Boheme, Vol. 1, Supp., pi. 2, fig. 19. 



