90 PALEONTOLOGY. 



dark-colored limestone. There are specimens in the collection, however, 

 from Fossil Hill, White Pine District, apparently belonging to this species, 

 in a lighter-colored matrix. Everywhere in Carboniferous beds; and either 

 the same or a closely-allied species occurs in the Coal-Measures of Illinois. 



Spibifer (Tbigonotbeta) scobina, Meek. 



Plate 9, figs. 1, 1 a, 1 &, 1 c, 1 d. 



Spirifera scobma. Meek (1860), Proceed. Acad. Nat. Sci. Philad., XII, 310. 

 Sjjirifer (Spiriferina?) scobina, Meek (1876), in Col. Simpson's Eeport Expl. across the 

 Great Basin of Utah, 351, pi. ii, figs. 5 a, b, c. 



Shell attaining a moderately large size, truncato-subcircular, or 

 approaching subpentagonal, rather gibbous, and more or less nearly equi- 

 valve, with length and breadth scarcely differing; hinge-line about equal- 

 ing, or a little less than the greatest breadth, and generally intersecting the 

 lateral margins at rather obtuse angles; outline of front rounded, a little 

 straightened, or probably sometimes slightly sinuous at the middle ; lateral 

 margins rounding to the front. Ventral valve generally a little more con- 

 vex than the other; beak not very prominent, but strongly incurved; area 

 well defined, of moderate breadth (height), and continued to the extremities 

 of the hinge, more or less arched and directed a little obliquely backward; 

 foramen wider than high; mesial sinus narrow and very shallow, but usually 

 continued nearly to the beak, occupied at the front by about five smaller 

 plications than those on the lateral slopes, the outer ones usually coalescing 

 with the larger marginal one on each side before reaching the beak; lateral 

 slopes each occupied by about eight rather depressed costse, which are wider 

 than the furrows between them, and sometimes, though rarely, bifurcate. 

 Dorsal valve with beak strongly incurved; mesial fold scarcely defined, 

 excepting at the front, where it is flat, and ornamented by about six much 

 depressed costge, which coalesce so as to reduce the number to three before 

 reaching the beak; lateral slopes each occupied by about eight to ten rather 

 broader, depressed, and sometimes bifurcating costse, as in the other valve. 

 Surface of both valves, when well preserved, showing very fine, obscure, 

 crowded, and undulating striae of growth, and everywhere covered with 

 closely and very regularly arranged granules, not generally readily seen 

 without the aid of a magnifier. 



