October, 1913. New Trilobites — Slocom 47 



DESCRIPTION OF GENERA AND SPECIES. 



Order OPISTHOPARIA. 



Family ASAPHID^E, Errimrich 



Genus ISOTELUS DeKay 1824. 



Cephalic and caudal shields of nearly equal size with broad infolded 

 margins; glabella nearly smooth, not lobed; free cheeks large, sometimes 

 meeting in front of the cranidium ; eyes prominent holochroal ; hypos- 

 toma deeply forked; thoracic axis wide; pygidium obscurely lobed, 

 segmentation often obsolete at maturity. This genus is distinguished 

 from Asaphus by the absence of the lobation of the glabella, the distinct 

 segmentation of the pygidial axis and the wider thoracic axis. 



Isotelus gigas DeKay. 



/. gigas DeKay, 1824. Ann. Lyceum Nat. Hist. N. Y., Vol. I, p. 

 174, pi. 12, fig. 1, pi. 13, fig. 1. 



I. gigas Clarke, 1897. Pal. Minn. Vol. Ill, pt. 2, p. 701 and 706. 



A portion of a pygidium from the Lower Maquoketa at Clermont 

 and one from the Upper Maquoketa at Patterson's Springs, on account 

 of their size are doubtfully referred to this species. These are the 

 representation of this species from Fayette County in the Museum 

 collection. The State University of Iowa has in its collection a nearly 

 complete individual of this species from the Maquoketa of Florence- 

 ville, Howard Co., Iowa, so that the species may be looked for in 

 Fayette County. 



Isotelus maximus Locke. 



/. maximus Locke, 1838. Sec. Ann. Rept., Geol. Surv., Ohio, p. 246, 

 figs. 8, 9. 



I. megistos Locke, 1841. Trans. Am. Geol. and Nat., p. 221. 



/. maximus Clarke, 1897. Pal. Minn. Vol. Ill, pt. 2, p. 701 

 and 706. 



This species is represented in the Museum collections by one cephalon 

 in which the specific characters are well shown and several pygidia which 

 probably belong to the species. They were found near the top of the 

 Lower Maquoketa beds at Clermont. Most of the specimens of 

 Isotelus from this locality which have been referred by other authors to 

 I. maximus are here referred to /. iowensis Owen. (See remarks under 

 that species.) 



