THE NATURAL HISTORY SURVEY. 



Illaenus cuniculus Hall, pi. xix, figs. 1-6. 



Description. Cephalon elongate, longitudinally semi-ellip- 

 tical in outline, depressed convex, anterior and lateral margins 

 slightly produced to form a narrow, projecting, lip-like, mar- 

 ginal border. Dorsal furrows slightly impressed, short, not 

 extending beyond the anterior extremities of the eyes. Eyes 

 of moderate size, about three times as long as high, subcres- 

 centiform in outline, convex longitudinally and vertically, 

 situated nearly horizontally or with the anterior extremity 

 slightly higher than the posterior, their centers above the middle 

 of the total height of the cephalon, and much nearer the pos- 

 terior than the lateral margins. Eye-lobes sloping downward 

 from the dorsal furrows, the cheeks sloping much more abruptly 

 from the outer margins of the eyes to the lateral border; just 

 outside the outer margin of the eyes upon the free cheeks, is a 

 slightly impressed, rounded furrow which is deeper and more 

 conspicuous posteriorly. The posterior limb of the facial 

 suture is very short, the anterior limb describes a slightly con-, 

 cave curve towards the front and intersects the margin almost 

 directly in front of the eyes; the sutures from opposite sides 

 are then continuous around the anterior extremity of the cepha- 

 lon upon the ventral side just within the margin. Free cheeks 

 rather large, longer than wide. 



The thorax and pygidium to be associated with this cephalon 

 have not been recognized. 



The dimensions of a small but nearly complete cephalon 

 are: length 20.5 mm., width 25 mm., convexity n mm., width 

 between the eyes 21.5 mm. The dimensions of a large crani- 

 dium are: length 42.5 mm., width between the eyes 50 mm. 



Remarks. This species may always be distinguished by 

 its depressed cephalon, by its short dorsal furrows and by the 

 posterior position of the eyes. In the short projecting lip-like 

 anterior and lateral border of the cephalon, the species resem- 

 bles /. insignis and /. harrisi, but the projection is less con- 

 spicuous upon /. cuniculus than upon either of the others. 

 The species does not usually grow so large as /. insignis. 



Locality. Hawthorn, Illinois. 



Illaenus niagarensis Whitfield, pi. xix, figs. 7-11. 



Description. Entire body elliptical in outline, trilobation 

 obsolete. Head and pygidium nearly equal in length, the 

 thorax shorter than either. Cephalon sub-elliptical in outline, 

 moderately convex, the dorsal furrows shallow and ill-defined 



