26 PALEONTOLOGY OF THE EUREKA DISTRICT. 



Agnostus bidens Meek. 

 Plate ix, figs. 13, 13 a. 



Agnostus bi(]cns Meek, 1873. Sixth Ann. Rep. IT. S. Geol. Surv. Territories for the 

 year 1872, p. 463. 



Cephalic shield, moderately convex; a little wider than long, distinctly 

 trilobed and bordered by a rounded margin, with a rather strongly defined 

 marginal groove. Glabella convex, narrow, more than two-thirds the 

 length of the shield, converging anteriorly and rounded or subangular in 

 front; a narrow, transverse furrow enters obliquely from each side poste- 

 rior to the center and unites just in advance of a small tubercle on the 

 center of a segment defined behind by a transverse furrow that bends back- 

 ward at the center; between the latter furrow and the occipital furrow, a 

 narrow segment widening out laterally, is distinctly defined; occipital seg- 

 ment very narrow. Dorsal furrows distinct, united in front of the glabella 

 but not touching the frontal border. Lateral lobes strongly convex and 

 sloping rapidly to the marginal groove from the somewhat elevated central 

 portion; frontal lobe about half as wide as the lateral lobes and less 

 convex. 



Thoracic segments unknown. 



The caudal shield associated with the above-described head has all of 

 its essential elements, and there is little doubt but that it belongs to the 

 same species. It is provided with a short spine or process on each posterior 

 lateral side and is strongly convex and trilobate; the axial lobe extends 

 more than three-fourths of the entire length and has an elongate, angular 

 node on the anterior portion, with a transverse furrow just before it separat- 

 ing a narrow anterior portion, and in some examples a slight transverse 

 furrow crosses just back of the node; this is obsolete in many instances. 

 The dorsal furrows extend backward and unite posteriorly, giving the axial 

 lobe a conical form; lateral lobes strongly convex and very much like 

 those of the associated cephalic shield. Surface of both shields finely 

 granulose under a strong magnifying power. 



