NO. 3 CAMBRIAN TRILOBITES 1 6/ 



Free cheeks large and shaped much Hke those of Menomonia (pi. 

 26, fig. ^d), except that they curve inward anteriorly so as to form 

 a narrow, slightly elevated portion that fitted against the side of the 

 projection in front of the glabella; as far as can be determined, the 

 eye was at the interior anterior end of the free cheek; posteriorly 

 the free cheek curves in against the fixed cheek in advance of the 

 genal angle. 



Dimensions. —A cranidium 7 mm. in length, including the narrow 

 frontal limb, has a width of about 16 mm. 



Genotype. — Dresbachia amata Walcott. 



Stratigraphic range. — As far as known, the genus is found only 

 in the sandstones of the Eau Claire and Franconia formations. 



Geographic distribution. — Upper Mississippi Valley; central and 

 western Wisconsin, and eastern Minnesota. 



Observations. — Of this genus we have only the cranidium and 

 free cheeks of one species. These indicate a type allied to Menomonia 

 calymenoides, although the cranidia differ greatly in the form of the 

 frontal limb and border and the free cheeks. The same is true of 

 Millardia (pi. 28, figs. 3, 3a, 4, 4a-b) in respect to the frontal limb 

 and border. The distinction between Dresbachia and Millardia is in 

 the character of the frontal limb and border. Dresbachia is unique 

 in the conformation of the narrow, deeply furrowed frontal hmb. 



DRESBACHIA AMATA, new species 

 Plate 26, figs. 5, 5a-c 



The description given of the genus Dresbachia includes what is 

 known of the species. It has hitherto been confused with Millardia 

 optata (Hall) (pi. 28, figs. 4, 4a-/), as the cranidia have similar 

 fixed cheeks and glabella, but differ very much in the form of the 

 frontal limb and border. 



The fragmentary remains of the cephalon are quite abundant at a 

 number of localities, but thus far I have not learned of an entire 

 dorsal shield having been found. 



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

 Claire formation; Eau Claire, Eau Claire County; (79) near Hud- 

 son, St. Croix County; (79X) Beaver Creek, north of Galesville, 

 Trempealeau County; (100) near Menomonie, Dunn County; and 

 ( looa) at Ettrick, Trempealeau County ; all in Wisconsin. 



Also from (84) Eau Claire formation ; Dresbach, Winona County ; 

 (84a) Franconia formation; River Junction, Houston County, Min- 

 nesota. 



