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138 CARBONIFEROUS PERIOD. 



England, wliicli Mr. Davidson illustrates on Plate XII, figs. 8, 9, and 10, 

 of his Monograph of British Carboniferous Brachiojjoda, and refers Avith 

 doubt to S. glabra. 



Position and locality. — Strata of the Cai-boniferous period; Camp Cotton- 

 wood, Lincoln County, Nevada. 



Genus SPIRIFERINA d'Orbigny, 1847. 



Spiriferina Kentuckensis Shumard. 

 Plate X, tig. 4 a, 1), and c. 



Spirifer octoplicaius Hall, 1852, Stausbxiry's Exped. Great Salt Lake, 409 (not S. octopli- 



cftiMsSowerby). 

 Spirifer Kentuckensis Shumard, 1855, Geol. Snrv. Missoiui, 203.- 

 Spirifer laminosus Geinitz, 1866, Carbouformat. imd Dyas iu Nebraska, 45 (not S. 



laminosus McCoy). 

 Spiriferina Kentuclcemis Meek, 1872, U. S. Geol. Surv. Nebraska, 185. 



Shell small, very variable in outline, usually sub semicircular, but some- 

 times the hinge-extremities are mucronate, and sometimes so shortened that 

 the shell is subglobose in form, but it is always broader than long. Ventral 

 valve more capacious than the other ; beak prominent, arching backward ; 

 area moderately high, well defined, concave ; foramen higher than wide ; 

 mesial sinus distinctly defined, rather narrow, often moderately deep, with- 

 out plications, except occasionally a small obscure one at the bottom. 

 Dorsal valve somewhat regularly convex ; beak scarcely j^rominent, pro- 

 jecting very slightly over the cardinal margin ; mesial fold narrow, dis- 

 tinctly defined, a faint linear depression sometimes observable along its 

 middle corresponding with the small linear plication sometimes seen at the 

 bottom of the sinus of the ventral valve. 



Surface of each valve marked by from ten to eighteen simple prominent 

 plications, roirnded or almost angular at top, and having interspaces of 

 similar width between them ; the plications bounding the sinus are a little 

 larger and a little more prominent than the othei'S, which thus serve to more 

 clearly define the sinus from the remainder of the shell. The entire surface 

 is also marked by fine, distinct, prominent, and closely-crowded lines of 

 growth. 



Length of a specimen, of" about average size and proportions, nine 

 millimeters ; breadth l)etween the liinge-extrcniitics, thirteen millimeters. 



