164 THE DEVONIAN OF MISSOURI. 



1861. Phacops rana Hall, Descriptions of New Species of Fossils, etc., p. 55. 

 1868. Phacops rana Meek and Worthen, Geol. Surv. Illinois, III, pp. 447-449, pi. 11, 



figs. 1 a-e. 

 1910. Phacops rana Grabau and Shinier, North American Index Fossils, II, p. 323, 



fig. 1638. 

 1913. Phacops rana Prosser and Kindle, Maryland Geol. Surv., Middle and Upper 



Devonian, pp. 329-331, pi. 43, figs. 8-12. 

 1913. Phacops rana Clarke and Swartz, Maryland Geol. Surv., Middle and Upper 



Devonian, p. 699, pi. 72, figs. 8, 9. 

 Description by Prosser and Kindle — "General form elongate suboval; greatest width 

 (measured at the posterior margin of the cephalon ) to axial length as 1 to 2 ; the cephalon, 

 thorax and pygidium are to one another in length as 1.5 to 2 to 1. Cephalon subsemi- 

 circular, the regularity of the outline interrupted by the slight protrusion of the glabella 

 and the genal extremities, frontal margin obscure, concealed by the overhanging gla- 

 bella; facial sutures rarely discernible; glabella large, gibbous outline subpentagonal, 

 greatest width anteriorly, posterior furrow extending clear across the glabella; cheeks 

 abruptly sloping to the margin, narrowing anteriorly and reflected ventrally to form the 

 doublure; eyes prominent, scarce reaching the height of the glabella in uncompressed 

 specimens, visual area lunate, separated from the cheek by a strong smooth sulcus, aver- 

 age number of lenses in normal adults is between forty and fifty for each eye. Thorax 

 subquadrate, lateral margins slowly tapering, surface strongly trilobate; axis flattened 

 at the margins, evenly convex in the middle, widest at the third or fourth segment, 

 tapering very slowly to the ninth, and thence much more rapidly to the pygidium ; pleurae 

 flat for about one-third their width from the axis and thence abruptly deflected to the 

 margin, each segment bears a furrow which becomes obsolete at the fulcrum. Pygidium 

 relatively small, regularly and evenly rounded margin the posterior part of which forms 

 the arc of a circle; axis composed of nine annulations, rapidly and evenly tapering from 

 the last segment of the thorax, reaching an acute termination just within the posterior 

 margin; pleurae seven in number, broad depressed-convex, and sloping evenly to the 

 posterior margin. Surface of the test ornamented with tubercles, which are largest and 

 most closely set upon the glabella." 



Remarks — Fragments from the sandstone member of the St. Laurent have been 

 referred to P. rana though no specimen is complete enough to make it possible to deter- 

 mine that it does not belong to P. cristata Hall. The reference is made to P. rana on 

 account of the age of the rocks in which it occurs. 



Occurrence — St. Laurent formation, \Yi miles west of Lithium, Perry County. 



VERTEBRATA 



Class PISCES 



Subclass Teleostomi 



Order Crossopterygii 



Family Onychodontidae 



Genus Onychodus Newberry 



Onychodus sigmoides Newberry 



Plate 39, figure 3. 



1857. Onychodus sigmoides Newberry, Proc. National Institute, Washington, D. C, 



new series, 1, p. 124. 

 1889. Onychodus sigmoides Newberry, Monograph U. S. Geol. Surv., 16, pp. 56-57, 



pi. 36, figs. l-4a; pi. 37, figs. 1-11. 





