276 THE CHICAGO ACADEMY OF SCIENCES. 



tending from the dorsal furrows to the inner edge of the mar- 

 ginal border. Head and thorax not known. 



The dimensions of a very perfect pygidium are: total 

 length to end of caudal spine 57 mm., length of axis 36 mm., 

 total width 67 mm., width of axis at anterior margin of pygidium 

 15 mm. 



Remarks. This pygidium has been observed from several 

 different localities and always attains about the same size, but 

 no heads have been seen which can be associated with it. In 

 general form the pygidium resembles that of D. verrucosus 

 Hall, more closely than any other species, but it does not have 

 the tubercles of that species and the marginal border is broader 

 and more conspicuous. 



Localities. Joliet, Bonfield, Chicago Drainage Canal near 

 Lemont. 



Dalmanites vigilans Hall, pi. xxiv, figs. 1-4. 



. Description. Cephalon moderately convex, semi-elliptical 

 in outline to the ends of the genal spines, with an anterior, 

 median, upwardly curving, spine-like extension, the entire 

 length of which has in no case been observed. Surface of the 

 glabella flattened back of the first pair of lateral furrows and 

 convexly curved to the front, wedge-shaped in outline, widest 

 in front, limited laterally by the dorsal furrows which are well 

 defined except opposite the posterior half of the first lateral 

 glabellar lobes, the entire glabella occupying about one-third of 

 the cephalon; frontal lobe transversely sub-elliptical in outline, 

 most strongly elevated at its posterior border, sloping to its 

 anterior border with a gently convex curve, occupying about 

 one-half of the entire glabella, its length about five-sevenths 

 its width; first lateral lobes wedge-shaped in outline, twice as 

 wide at their outer margin as within, their posterior halves 

 confluent with the cheeks across the dorsal furrows; second 

 lateral lobes quadrangular, smaller than the first and some- 

 what confluent with them externally; third lateral lobes similar 

 to the second but slightly smaller and wholly separate from 

 them; first lateral furrows directed obliquely outward and 

 forward, not continuous across the median portion of the 

 glabella, their inner extremities in front of the anterior margins 

 of the eyes, most deeply impressed internally, becoming nearly 

 obsolete at the dorsal furrows; second lateral furrows nearly 

 transverse in their direction, not continuous across the median 

 portion of the glabella, deeply impressed 'within, becoming 



