NO. 3 CAMBRIAN TRILOBITES 163 



Whitfield's description of the cranidium and thorax as far as he 

 knew it is very full and does not need to be repeated in detail. The 

 cranidia are abundant in the Eau Claire sandstone at Rock Falls, 

 Wisconsin, and the associated free cheeks which appear to belong 

 to them. One of these, illustrated by figure 4d, plate 26, has a small 

 eye, and a strong marginal rim that curves backward to join the 

 border of the posterolateral limb in advance of the genal angle ; 

 this is rounded as seen on the right side of figure 4, plate 26. 



Whitfield described an incomplete thorax having 22 segments. 

 The specimen illustrated by figures 4b and 4c has 42 thoracic seg- 

 ments, the dorsal shield narrowing very gradually from the cephalon 

 to the pygidium. 



Pygidium minute ; axial lobes short and divided into two or three 

 rings and a terminal section by shallow transverse furrows ; pleural 

 lobes smooth as far as may be determined from the cast in a fine 

 sandstone matrix. 



Exterior surface unknown except that the casts in fine sandstone 

 are nearly smooth. 



A specimen of the thorax and pygidium is 25 mm. in length. A 

 cephalon of the width to correspond to the anterior segments of the 

 thorax has a length of 7 mm. The largest cranidium in the collection 

 has a length of 10 mm. 



Observations. — The general characters of the species are included 

 in the description of the genus. 



Formation and locality. — Upper Cambrian: (78a and 98) Eau 

 Claire formation; near Eau Claire, Eau Claire County; (83a) Rock 

 Falls, and (100) Menomonie, Dunn County; also from (83*) 

 Dresbach formation; lower beds just above the river, Trempealeau, 

 Trempealeau County, both in Wisconsin. Also from (84) Eau Claire 

 formation ; Dresbach, Winona County, Minnesota. 



MILLARDIA, new genus 



General form elongate elliptical ; convex ; axial and pleural lobes 

 strongly defined. 



Cephalon transversely broadly elliptical with genal angles rounded ; 

 margined with a rounded distinct border and intramarginal furrow ; 

 glabella subtriangular in outline, convex, and marked by three pairs 

 of short lateral furrows ; occipital ring and furrow strongly defined ; 

 frontal limb short, slightly convex, and depressed between the gla- 

 bella and the strong rounded frontal border ; frontal border arched 

 upward between the points cut by the facial sutures ; fixed cheeks 



