226 PALEONTOLOGY. 



seems unnatural to thus refer them. On the other hand, they so closely 

 resemble the corresponding parts of the genus Bikellocephalus from the sand- 

 stone of the Mississippi Valley, that it has been deemed safer to refer them 

 to that genus, although no other parts recognized as belonging to the genus 

 have been observed. It is even more than probable, however, that, on 

 examining a larger collection of material from this locality, other parts of 

 the organisms will be found justifying this reference, as there are many 

 fragmentary portions of undetermined species in the few blocks now before us. 



HlKELLOCEPHALUS BILOBATUS U. Sp. 



Plate II, fig. 36. 



Pygidium transA^erse, irregularly oval, rather straight on the anterior 

 border, rounded and deeply bilobed on the posterior margin by a sharply 

 angular constriction of the posterior border on the median line, extending 

 to the extremity of the axial lobe; marginal lobes rounded on their pos- 

 terior extremities. Axis comparatively small, moderately convex, marked 

 by six or seven transverse rings, exclusive of the terminal ones. Lateral 

 lobes broad, rounded behind, and wing-like, slightly convex on the under 

 surface, and recurved toward the border; marked by four ribs on each side, 

 which appear to have been obscurely divided, and do not extend to the 

 margin of the shield. On the under surface, the posterior border is inflected^ 

 forming a very wide inner rim, or lining, occupying nearly one-half the area 

 of the lateral lobes. Surface apparently smooth. 



The deeply bilobed character of the posterior border is a marked and 

 distinguishing feature. 



Formation and locality. — In limestone of the Potsdam group, in the Eureka 

 District, Nevada. Collected by Arnold Hague, esq. 



DiKELLOCKPHALUS MULTICINCTUS 11. Sp. 

 Plate II, fig. 37. 



Pygidium somewhat triangular in general form, or, considering the 

 anterior border as consisting of two sides, would be somewhat trapezoidal ; 

 front margin arcuate, a little angular on the shoulders, and more rapidly 

 declining toward the outer extremities ; the entire front nearly semicircular; 

 posterior margin extended in the direction of the median line, and present- 

 ing the appearance of having been digitate on the lateral borders. Thi's 



