418 REPORT ON THE STATE CABINET. 



CRUSTACEA. 



In the Annual Report on the Geology of Wisconsin for 1860 (pub- 

 lished in 1861), I described two new species of Ill^nus, a new Calymene, 

 and a species of Dalmanites,* and in the list of species appended to the 

 Geology of Wisconsin, Vol. i, p. 423, I noticed a species of Acidaspis (tI. 

 danai) from the limestone of the Niagara group. 



A farther study of the collections in my possession, from the limestones of 

 Racine, Waukesha, and from near Milwaukee, with a few from Illinois, has 

 shown several other trilobites ; among which the following may be noticed. 



GENUS ILL^NUS, Dalman. 

 Ill^nus armatus, n. s. 



PLATE XXII, FIGS. 1-3; PLATE XXV, FIG. 22. 



Head short and gibbous, varying in its proportions from nearly twice as 

 wide as long, to length equalling two-thirds the width ; elevated in 

 the centre. The dorsal furrow makes a short rounded arch from 

 the base of the shield, and terminates in a perceptible impression, 

 on a line with the base of the eye and half way between it and the 

 anterior margin. Eyes very prominent, situated close to the pos- 

 terior margin ; palpebral lobe short ; furrow above it scarcely longer 

 than the sinus below the eye. Cheeks small, making not more than 

 one-fo>irth of the width of the head, and the suture coming to the 

 anterior margin a little in advance of the eye. The posterior 

 angles prolonged into short spines which extend directly backwards. 

 The pygidium in several specimens has the proportions of length 

 and breadth as 5 to 7, 6 to 8, and 7 to 10. The largest head iden- 

 tified as belonging to this species has a length of about one inch. 



In fig. 8, the head is represented fig. s. 



of the natural size, and fig. 9 is a 

 profile view of the same. 



Compared with lllcenus {Bumas- 

 tus) harriensis, the head is more 

 prominent in the middle, more produced in front, and the eyes 



* TlUenus imperator of the Niagara group, /. taurus of the Trenton Umestone, Calymme mam- 

 millata of the Hudson river group, and Dalmanites vigilans of the Niagara group. 



