102 PALAEONTOLOGY. 



Locality and position. — "West of New Pass Mines, Desatoya Mountains, 

 Cottonwood Canon, West Humboldt Range, Nevada. 



LUOINIDJ^. 



Genus SPH^RA, Sowerby. 



Sph^ra Whitneyi, Meek. 



Plato 10, figs. 4, 4 a, 4 Z>, 4 c. 



Shell subcircular, almost exactly equilateral, rather convex, basal, ante- 

 rior, and posterior margins forming' together a regular semicircular curve; 

 dorsal margin somewhat straightened and nearly horizontal, or apparently 

 sometimes sloping shghtly from the beaks, rounding rather abruptly into 

 the anterior and less distinctly so into the posterior margins; beaks rather 

 depressed, or moderately prominent, obtuse, nearly central, and with^^ut 

 visible general obliquity, but with the incurved immediate points directed a 

 little obliquely forward; surface only showing obscure lines of gi'owth. 



Length of largest specimen seen, 1.65 inches; height, 1.54 inches; con- 

 vexity, 0.86 inch. 



None of the specimens of this shell give any clew to the nature of its 

 hinge or interior; but, from its general external characters, I am led to refer 

 it to SphcBra, though I am aware that it might, so far as can be seen, with 

 almosl. equal propriety be refeiTcd to Unicardium, or any one of several other 

 genera. Some varieties of it resemble Lucina anceps of Laube (see Fauna 

 der Sch. von St. Cassian, taf. xv, figs. 4, 4 a); but it is evidently not a Lu- 

 cina. It also differs in attaining a much larger size, and in wanting the 

 peculiar sinuous character of the anterior ventral margin, so distinctly marked 

 in Laube's shell. 



It is possible that our largest specimen represented by fig. 4 c may be 

 a distinct species from the smaller typical fonns repi'esented by figs. 4 and 4 a. 



Locality and position. — Buena Vista Caiion, West Humboldt Range, Ne- 

 vada; Upper Trias. 



