248 PALAEONTOLOGY. 



in the same pcarticulars, as well as the finer and more numerous plications, 

 and in the want of the flattening of these latter on the front of the shell. 



Formation and locality. — In limestones of Devonian ag-e, south of Aurora 

 Mine, "White Pine, Nevada. Collected by Arnold Hague, esq. 



LAMELLIBEANCHIATA. 



Genus PARACYCLAS Hall. 

 Paeacyolas peroccidens n. sp. 



Plato III, figs. 14-17. 



Shell comparatively large, circular in outline, with scarcely projecting, 

 but well-marked beaks; valves ventricose, somewhat inflated along the 

 strongly-curved or convex umbonal ridge; cardinal line strongly arcuate, 

 but becoming slightly alate toward the posterior end, especially perceptible 

 on the internal casts; anterior side of the shell marked by a slight constrict- 

 ing sulcus, or depression, extending from the front of the beaks to the margin 

 of the shell just below the middle of the anterior side, strongly reminding 

 one of the similar constriction on mau}^ of the recent Lucinas; beaka pointed 

 and strongly curving forward, situated well anteriorly. On the internal 

 casts, the muscular impressions are large and strongly marked, the posterior 

 one is irregularly quadrangular, and the anterior one reniform, widening 

 below, and not more than half as large as the posterior; pallial line consist- 

 ing of strong longitudinal pustules, arranged side by side. 



Surface of the shell somewhat roughened by strong, irregular, but not 

 lamellose, concentric undulations formed by aggregating lines of growth. 



The shell differs from any form previously described in this country in 

 the presence of the anterior constriction, but, in many other respects 

 resembles P. elliptica var. occidentalis II. & W., from the Upper Helderberg 

 limestones of Southern Indiana. 



Formation and locality. — In dark limestone of Devonian age, at Treasure 

 Ilill, south of Aurora ]\Iine, Wliite Pine. Collected by Arnold Hague, esq. 



Genus NUCULITES Conrad. 

 Ntjculites trianguliis u. sp, 



Plato III, figs. 12-13, 



Shell comparatively large for the genus, subtriangular in outline, about 



