THE NATURAL HISTORY SURVEY. 259 



segment 6 mm., length of eye-stalks 7.5 mm. The dimensions 

 of a large pygidium are: length, exclusive of caudal spine 29 

 mm,, length of spine 10.5 mm., width at anterior margin 18 

 mm., width of axis anteriorly 7 mm. 



Remarks. This species is remarkable by reason of its elon- 

 gate eye-pedicles. These eye-stalks are difficult to preserve, 

 and are usually broken off either before the creatures were 

 fossilized or by the collectors of the specimens, this being the 

 condition of the type specimen used by Miller in his description 

 of the species. The thoracic and caudal spines are also usually 

 broken. The species is so different from any of the other species 

 of the genus that no comparison with any of them is necessary. 



Localities. Joliet, and Chicago Drainage Canal near Le- 

 mont. 



Encrinurus tuberculifrons, n. sp., pi. xxiv, figs. 12-13. 



Description. Cranidium sub-triangular in outline. The 

 glabella prominent, sub-pyriform, not produced in front be- 

 yond the anterior margin, bounded by deep dorsal furrows; 

 lateral furrows three on each side, not continuous across the 

 median portion of the glabella, but the posterior pair more elon- 

 gate than the others; occipital furrow well defined entirely 

 across the posterior margin of the glabella, the occipital seg- 

 ment narrow; in front the glabella is bordered by a narrow flat- 

 tened marginal border. Fixed .cheeks strongly convex, with 

 deep posterior cheek furrows originating at the dorsal furrows 

 opposite the lateral extremities of the occipital furrow and ex- 

 tending nearly to the genal angles; genal angles apparently 

 rounded and not produced into genal spines; eye-lobes small, 

 elevated. Free cheeks not known. The entire surface of the 

 glabella and fixed cheeks, except the occipital segment and the 

 posterior marginal border of the cheeks, covered with small 

 rounded tubercles, the anterior marginal border in front of the 

 glabella bears a single continuous, symmetrically arranged row 

 of tubercles similar to those upon the convex portion of the 

 glabella. 



Pygidium sub- triangular, wider than long, not produced 

 posteriorly into a caudal spine. The axis prominent, bor- 

 dered by well defined axial furrows, extending nearly to the 

 posterior margin, its width in front about one-third the total 

 width of the pygidium, marked by about fifteen annulations 

 which become finer and less distinct posteriorly. Pleural lobes 

 a little flattened adjacent to the axial furrows, the surface curv- 



