CAMBRIAN TRILOBITES — WALCOTT 21 



widens gradually and passes directly into the terminal spine ; the 

 posterior border is a narrow, rounded ridge that merges into the 

 base of the terminal spine. 



Pygidium moderately convex, about one-fourth of the length of 

 the dorsal shield, elongate, semicircular in outline; axial lobe con- 

 vex, divided by five shallow, narrow, transverse furrows into five 

 rings and a terminal section that is within the border ; pleural lobes 

 marked by the pleural furrows of four anchylosed segments that 

 merge into the smooth border ; a slender but strong, long spine ex- 

 tends from a strong base on each side of the p3^gidium; this spine 

 appears to be the extension of the anterior anchylosed segment. 



Surface finely granulose, with scattered larger granules on small 

 specimens. 



Dimensions. — A dorsal shield 40 mm. in length has the following 

 dimensions : 



Cephalon : mm. 



Length 13 • 5 



Width at posterior margin 31.5 



Thorax : 



Length 17 -o 



Width at first segment 22 . 



Pygidium : 



Length 9-5 



Width 15-0 



Observations. — A dorsal shield 2.7 mm. in length, with a cepha- 

 lon 2.3 mm. long, has a fixed cheek nearly as wide as the glabella, 

 an eye lobe fully one-half the length of the cephalon, and the glabella 

 slightly expanded toward the front. A large cranidium, 23 mm. 

 in length, has a glabella proportionally wider in front, and very 

 strong, posterior, oblique furrows. 



This species was first found in 1904, on Gordon Creek, Ovando 

 Quadrangle, Montana, in argillaceous shales, a short distance above 

 the supposed Flathead sandstones, in association wuth 



Acrothele colleni, new species, 



Wimanella simplex, new genus and new species, 



Olenopsis, 



Ptyclioparia. and 



Bathynriscus, sp. a. 



The stratigraphic position of this subfauna was not determined 

 in Montana, owing to the break in the continuity of the section on 

 Gordon IMountain. 



The specific name is given in recognition of the discovery by Mrs. 



