27O THE CHICAGO ACADEMY OF SCIENCES. 



with ten segments. Pygidium small, with three pairs of pleural 

 segments which are produced distally in backwardly pointing 

 free points. 



Staurocephalus obsoleta, n. sp.. pi. xxiv, fig. 15. 



Description. Cephalon, exclusive of the anterior extension 

 of the glabella, sub-semicircular in outline, the postero-lateral 

 angles produced into rather short but slender genal spines. 

 Glabella narrow in its posterior portion, sharply arched trans- 

 versely, bounded by deep and strong dorsal furrows, tapering 

 gently from the occipital furrow to a point nearly above the 

 frontal margin of the cephalon, from this point the frontal 

 lobe of the glabella expands abruptly into a large globular 

 extension beyond the frontal margin of the cephalon, the 

 diameter of the globular frontal lobe being equal to one-half 

 the total length of the cephalon; lateral glabellar furrows and 

 lobes obsolete; occipital furrow shallow, rounded in the bottom; 

 occipital segment narrow, strongly arched transversely. Cheeks 

 sub-triangular in outline with an ill-defined, rather broad, 

 marginal border, the eyes elevated nearly to the level of the 

 glabella, facial sutures not distinguishable; in front of the 

 eyes the surface of the cheek drops away nearly perpendicularly 

 to the frontal margin, laterally the slope is very abrupt but 

 not quite perpendicular, posteriorly and towards the dorsal 

 furrows the slope is gentle ; the outer margin of the cheeks is 

 bordered by a row of fine, fringe-like spines, there being about 

 twelve on each side between the genal angle and the base of 

 the globular frontal lobe of the glabella. Thorax and pygidium 

 not recognized. 



The dimensions of the type specimen are: total length of 

 head along median line 6 mm., length of globular frontal lobe 

 of the glabella 4 mm., maximum width of head 9 mm. 



Remarks. This species is one of the rarest trilobites in the 

 Chicago fauna, a single specimen only having been observed. 

 The species is a close ally of the European S. murchisoni Barr., 

 but it may be distinguished from that species by the obsolete 

 lateral glabellar furrows. 



Locality. Chicago Drainage Canal, near Lemont. 



Family 10. PHACOPIDAE Salter. 



"Glabella tumid, widest in front. Free cheeks continuous, 

 united anteriorly. Suture extending from in front of the genal 

 angles inward to the eyes, and thence forward around the 



