RAYMOND: NEW AND OLD SILURIAN TRILOBITES. 17 



BuMASTUS NiAGARENSis (Whitfield). 

 Plate 1, fig. 3. 



Illaenus niagarensis Whitfield, Ann. rept. Geol. surv. Wisconsin for 1879, 1880, 



p. 68. Weller, Bull. Chicago acad. sci., 1907, no. 4, pt. 2, p. 219, pi. 19, 



f. 7-11. 

 Illaenus madisonianus Whitfield. Geol. Wise, 1882, 4, p. 307, pi. 20, figs. 8-9. 



Foerste, Bull. sci. lab. Den univ., 1885, 1, p. 106 pi. 14, f. la-b, 2a-b; 



1887, 2, p. 93, pi. 8, f. 8, 9, 10, 10a; Geol. surv. Ohio, 1893, 7, p. 526, pi. 



26, f. 1, 2, varieties, pi. 27, f. 7-10. Van Ingen, School of mines quar- 

 / terly, Columbia univ., 1901, 23, p. 35. 



This seems to be one of the few illaenids of the Chicago-Wisconsin 

 Niagaran area which has hitherto been known from entire specimens. 

 Whitfield figured an entire one, Weller had a nearly complete speci- 

 men, and there are five in the M. C. Z. (Day collection). One of 

 these is figured as it shows some characters not shown in either Whit- 

 field's or Weller's figure. Whitfield's figure, if it really represents this 

 species, is inaccurate in respect to the glabellar furrows, which are 

 really much longer than is indicated by his figure or description. 

 From the general proportions of the body, and the position of the eyes, 

 it would seem that his figure really does represent this species. The 

 specimen here figured is a little longer and narrower than those 

 previously figured, and has a longer and more pointed pygidium. 



It will be noted that the thoi'ax is exceedingly short, though ten 

 segments are present. The dorsal furrows do not show in the figured 

 specimen, but they do on another specimen in the M. C. Z. collection, 

 and are also indicated in Whitfield's figure. 



The specific characteristics are : — cephalon rather convex, with 

 long dorsal furrows, no lip or concave border on the cephalon. Eyes 

 of medium size, situated nearly their own length from the posterior 

 margin, thorax short, pygidium long, rather pointed behind, with 

 narrow concave border. 



Measurements: — The specimen (Plate 1, fig. 3) is 58 mm. long; 

 cephalon 22 mm. long, 31 mm. wide; thorax 13.5 mm. long; pygidium 

 29 mm. long, 29 mm. wide; the eyes are damaged. On a very good 

 enrolled specimen preserving the test, the cephalon is 24 mm. long, 

 the eye 5 mm. long, and 5 mm. from the posterior margin. On a 

 larger specimen the eye is 1 mm. more than its own length from the 

 posterior margin. 



