DESCRIPTION OF GENERA AND SPECIES. 221 



Genus ASAPHISCUS Meek. 



Aaipliiscus MEEK, 1873. (See Walcott, 1886, Bull. U. S. Geol. Survey, No. 30, p. 219.) 



Asaphiscus iddingsi Walcott. 



Plate 23, Figures i, \a-b. 



Asaphiscus iddingsi WALCOTT, 1911, Smithsonian Misc. Coll., vol. 57, No. 4, pp. 99-101, plate 16, 

 fig. 3. (Described and discussed as a new species essentially as below.) 



Dorsal shield longitudinally oval in outline, moderately convex. Cephalon 

 semicircular in outline ; a little more than one-third of the entire length of the dorsal 

 shield ; bordered by a nearly flat or slightly rounded margin that passes at the genal 

 angle into a moderately strong genal spine; within the genal spine a rounded 

 posterior border is separated from the fixed cheek by a rounded, clearly defined 

 furrow; the intermarginal furrow is shallow and rounded. Cranidium moderately 

 convex and roughly subquadrate in outline; the frontal limb is slightly convex and, 

 with the anterior portion of the glabella and the front margin, forms a gentle slope 

 that is broken only by the slight dorsal furrow in front of the glabella and the 

 shallow intermarginal furrow; the frontal limb merges on the sides into the fixed 

 cheeks, which are a little less than one-half the width of the glabella; posteriorly 

 the fixed cheeks merge into relatively small postero-lateral limbs; palpebral lobe 

 narrow and extended in front as a low ridge that crosses the fixed cheek to the 

 dorsal furrow near the antero-lateral angle of the glabella; that portion of the 

 palpebral lobe above the eye is about one-fourth the length of the cephalon. 



Glabella large, slightly narrower in front than at the occipital furrow; sides 

 nearly straight and slightly converging, frontal margin broadly rounded; surface 

 marked by very faint impressions of three pairs of glabellar furrows, which can only 

 be seen where the surface is very perfectly preserved. Occipital ring about as wide 

 as the frontal margin and separated from the glabella by a shallow furrow that 

 terminates on the side slightly in advance of the posterior intermarginal furrow. 

 Free cheeks about as wide opposite the eye as the fixed cheeks; eye-lobe about 

 one-fourth the length of the cephalon. Postero-lateral angle continued backward 

 into a moderately strong spine. The facial sutures cut the posterior margin just 

 within the genal angle and extend obliquely inward with a slightly sigmoid curvature 

 to the base of the eye-lobes; curving over and around the eye-lobes, they pass 

 forward and a little outward, cutting the frontal margin obliquely. 



Thorax with nine segments; axial lobe moderately convex, slightly narrower 

 than the pleural lobes in compressed specimens ; on the outer side of each segment 

 a low, rounded node or ridge is separated from the main body of the segment by a 

 slightly oblique furrow transverse to the segment; pleural lobes slightly convex, 

 nearly flat out to the geniculation, where they curve slightly downward and back- 

 ward ; each pleura has a well-defined furrow starting near the inner anterior margin 

 and extending backward to the center of the pleura at the geniculation, where it 

 curves slightly backward and terminates on the broadly rounded, slightly falcate 

 end of the pleura. 



Pygidium roughly semicircular in outline, one-fourth the length of the dorsal 

 shield; anterior margin nearly transverse at the axial lobe and curving slightly 

 backward to conform to the curvature of the last thoracic segment; axial lobe 

 moderately convex and tapering gradually toward its posterior section, which is just 

 within the nearly flat marginal border ; it is divided by four transverse furrows into 

 four rings and a terminal section; three anchylosed pleural segments are outlined 

 on the pleural lobes by furrows that curve backward and terminate on the inner 

 margin of the doublure; this line is continued forward on the pleural lobes of the 

 thorax, terminating on each side opposite the posterior end of the facial suture. 



