258 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



Dorsal shield large ; gently convex as preserved in the arenaceous 

 shales ; broadly ovate in outline. Cephalon transversely semicircular 

 in outline, one-third the length of the adult dorsal shield ; bordered 

 by a narrow, wire-like rim that is extended at the genal angles into 

 a slender spine ; intergenal angles distinctly shown in adult specimens 

 [fig. 3, pi. 2T,]. Glabella about four-fifths of the length of the 

 cephalon ; it narrows from the occipital segment towards the frontal 

 lobe, as shown bv figs. 2 and 3 ; in a small specimen of the cephalon 

 3.75 mm. in length it is almost cylindrical, with the sides convergmg 

 slightly toward the front; the anterior lobe is about two-fifths the 

 length of the glabella and narrower than the lobes posterior to it ; 

 it was evidently convex before being flattened in the shale, and nar- 

 rowed toward the front ; the three posterior transverse lobes de- 

 crease- in size from the front to the posterior lobe, and slope from 

 each side gently backwards toward the center ; the glabellar furrows 

 are narrow and in the specimens available for study are united at the 

 center bv a shallow groove. Occipital segment transverse, stronger 

 than the posterior segment of the glabella and separated from it by 

 a narrow, clearly defined furrow. 



Eye lobe long, crescentiform, broad at the base and extending 

 from opposite tlie back portion of the anterior lobe of the glabella 

 back to nearly opposite the occipital furrow ; it is united, even in 

 large adult specimens, by a strong ridge to the frontal lobe of tlie 

 glabella [fig. 3], very much in the same manner as in small cephalons 

 of EUiptoccpliala asaphoidcs [pi. 24, figs. 3, 4, 6, and 7] ; the pos- 

 terior end of the eye lobe is rather close to the dorsal furrow be- 

 tween it and the glabella. Cheeks broad, large, and beautifully 

 marked on the interior surface by a system of irregular canals ex- 

 tending from the base of the eye lobe toward the outer margin 

 [fig. 6]. 



Thorax elongate, tapering gently from the cephalon to the py- 

 gidium. It has twenty-eight segments, the anterior seventeen of 

 which are progressively smaller, but otherwise uniform in character ; 

 these may be designated as the normal segments of this species ; the 

 posterior eleven segments have only the curved spinose extension of 

 the segment bevond the axial lobe, the body portion of the pleural 

 lobe not appearing liack of the seventeenth segment. In a small 

 dorsal shield with a cephalon 3.75 mm. in length the pleural lobes 

 disappear beside the axial lobe at about the tenth segment from the 

 cephalon. L'n fortunately, the posterior segments are broken off. 

 The axial lobe is convex ; less than one-half the width of the pleural 



