04 PALEONTOLOGY OF THE EUREKA DISTRICT. 



are preserved in the specimen before us, with a third partially shown ; the 

 outer ones embrace but little of the inner; they are somewhat flattened and 

 apparently sharply rounded on the ventral lobe. Umbilicus wide, exposing 

 all the inner volutions. The volutions enlarge very gradually until towards 

 the outer portion of the last volution, or the grand chamber, where the ex- 

 pansion is slightly increased. 



The entire dimensions of the chamber of habitation are unknown, as a 

 portion is broken away and the latter septa are partially concealed by the 

 test ; the part remaining, however, indicates that it was large. Four septa 

 are seen on the outer volution, obtained by cutting away a portion of the 

 test ; they are thin and uniform, curving a little forward on the umbilical 

 margin and then gently curving backward, including a single broad, flat- 

 tened lobe which occupies the entire width of the volution. Ventral lobe 

 unknown. Test thin. 



Surface marked by strong striae and lines of growth that curve forward 

 from the umbilicate lobe, crossing the direction of the septa at an acute an- 

 gle near the umbilical margin and nearly at right angles on the outer por- 

 tion of the volution. 



This species differs in its wide umbilicus united with the direction of 

 the surface striae and septa from any form that has come within our obser- 

 vation. 



Formation and locality. Devonian limestone, Comb's Peak, Eureka 

 District, Nevada. 



CRUSTACEA. 



Genus BEYRICHTA McCoy. 



Beyrichia (Primitia) occidentalis, n. sp. 



Plate xvii, figs. 4, 4 a. 



Carapace large, Leperditia-like in outline, 4 5 mm in length by 2.75 mm in 

 breadth ; strongly convex ; dorsal margin slightly incurved two-thirds the 

 length of the valves and terminating anteriorly and posteriorly in obtuse 

 angles formed by its union with the anterior and posterior margins ; ventral 

 margin gently curved to its union with the broadly rounded anterior and 

 posterior margins. Two deep and slightly curved sulci penetrate the cen- 



