THE NATURAL HISTORY SURVEY. 263 



Localities. Bridgeport, Hawthorn, Joliet, near Lemont, 

 etc., etc. 



Family 9. CHEIRURIDAE Salter. 



"Glabella well defined. Free cheeks small, sometimes 

 much reduced. Sutures extending from in front of the genal 

 angles inward to the eyes, and then obliquely forward, cutting 

 the anterior margin in front and on each side of the glabella. 

 Eyes usually small. Thorax of from nine to eighteen segments, 

 generally eleven; pleura often extended into hollow spines. 

 Pygidium. small, with from three to five segments; pleural 

 elements commonly produced into spines." Beecher, Zittel- 

 Eastman Text Book of Paleontology, p. 635. 



Genus 16. CERAURUS Green, 1832. 



Entire body sub-ovate in outline. Cephalon sub-semi- 

 circular or sub-semielliptical in outline, the genal angles pro- 

 duced into spines; glabella strongly convex, broadest in front, 

 with three pairs of deep, lateral furrows; posterior limbs of the 

 facial sutures cutting the lateral margins well in front of the 

 genal angles; eyes small. Thorax usually with eleven segments, 

 rarely nine to thirteen; axis prominent, narrower than the 

 pleura, bounded by strong axial furrows. Pygidium small, the 

 pleural segments produced into points or spines. 



Ceraurus niagarensis Hall, pi. xx'V. figs. 20-21. 



Description. Head sub-circular in outline with slender 

 genal spines projecting straight backward. Glabella mod- 

 erately convex, broadest in front, limited by well-defined, im- 

 pressed dorsal furrows, its posterior margin occupying one-third 

 of the total width of the head; frontal lobe transversely sub- 

 elliptical, occupying less than one-half of the entire glabella, 

 first lateral lobes small, sub-quadrangular; second lateral lobes 

 larger than the first, narrowest at the dorsal furrow; third lateral 

 lobes sub-triangular, entirely isolated; first lateral furrows 

 strong and deep, rounded in the bottom, directed a little back- 

 ward at their inner extremities, extending less than half way 

 from the dorsal furrow to the median line of the glabella ; second 

 lateral furrows similar to the first but a little shorter, their di- 

 rection nearly transverse; third lateral furrows strong and deep, 

 continuous across the glabella, shallower in the median portion 

 and arching backward to become confluent with the -occipital 

 furrow; occipital furrow about equaling in strength the lateral 

 furrows of the glabella, its median portion shallower and arching 



