(J(irh(ii(if('roii,s Trilobitc^. 75 



point is placed Hie large compound reniforni eye, which is eitlier sniooth or 

 facetted according to the state of its preservation. 



The segments of tlie thorax vary from 8 to 10. The axis is always strongly 

 arched, and does not exceed the pleur;e in breadth ; the breadth of the axis 

 diminishes very gradually to the posterior extremity. The pleurae are more 

 or less bent at the fulcral point, and have their extremities either pointed or 

 rounded and their anterior margin facetted. 



The pygidium varies in its elevation, but the axis is always raised above 

 the margin, and diminishes to a blunt extremit}^ leaving <a smooth bordei- 

 beyond. The number of lateral ribs varies from 4 to 13. The lateral ribs 

 do not extend to the margin of the pygidium. The contour of the pygidium 

 is often encircled with a border ; in some species the border is ornamented 

 with points {Phadoit, Archiaci, Barr). The surface of the test is most fre- 

 quently smooth or finely granulated ; in a few species it is striated, although 

 in some it is both striated and 2:ranulated. 



PROETUS MISSOUKIENSIS, Sliumard 



PI. Ill, Fig. 1. 



Compare Pivetus auriculatas, Hall, 1862, loth Rep. N. Y. State Cab. Nat. 



Hist., p. 107. 

 Pi'oetiis Missoiiriensis, Shumard, 1855, Geol. Sur. Missouri, p. 196, pi. B, 



tigs. 13 a, h. 



Proetus Musoiu'ieiisis, Vogdes, 1887. Bibliography Palaeozoic Crustacea. 

 Phillipsia Shumardi, Herrick, 1887, Bull. Sci. Lab. Dennison Univ., p. 58. 



Dr. Shumurd gives the following description of tliis species: 



" Glabella tumid, greatest height about the centre, ovoid, obtusely rounded 

 in front, truncated posteriorly, length a little greater than the width, widest 

 behind, three furrow^s on each side, posterior pair strongly marked ; these 

 commence at the dorsal sinus, about one-third the distance from base to 

 front, pass in a curve backwards, and bifurcate about midway between the 

 centre and sides of the glabella ; one branch very shallow, is continued for 

 a short distance almost transversely ; the other bends backwards nearly to 

 the occipital sinus, and with the main branch partially encloses a large oval 

 lobe on each side, the lobes separated by a space about half the width of the 

 glabella ; middle pair of furrows, shallow^ curving backwards in a direction 

 nearly parallel with the posterior ones, but considerably shorter ; anterior 

 pair feebl}" impressed, a little oblique ; occipital sinus a little convex to- 

 wards the front, shallowest in the middle ; occipital ring wide, flattened, 

 much lower than the plane of the glabella. Pygidium semi-circular, flat- 

 tened convex, width double the length, margin broad and slightly concave ; 

 axial lobe almost as wide as the lateral lobes, rounded at the extremity ; 

 segments ten, separated by strongly marked furrows ; lateral lobes flattened. 



