21 



species. The speciraeus were associated with the charjicteristic Carbon- 

 iferons or Ooal-Measure species, while the type-specimens of Meek aud 

 Worthen were obtained from the Chester limestone of the Subcarbou- 

 iferons series in Illinois. 



Genus Sptrifeeina d'Orbigny. 



Spiriferina spixosa var. ca^ipestris. — The collection contains 

 specimens of a species of Spiriferina from near Santa Fe, New Mexico, 

 and Camp Cottonwood, Lincoln County, Nevada, that correspond in all 

 essential respects with S. spinosa Norwood and Pratten, except that the 

 specimens show none of the minute spines of that species. These speci- 

 mens were found associated with species that are characteristic of the 

 Upper Carboniferous period, while theirs were collected from the Chester 

 limestone of Illinois of the Subcarboniferous series. It seems probable 

 that both this and the foregoing species survived from the Sul)carbou- 

 iferous to the Upper Carboniferous period, with comparatively little 

 change. 



Genus Dielasma King. 



DiELASMA ? BOYIDEXS MortoD (sp.) The species, so widely distri- 

 buted in the Carboniferous rocks of the United States, and so widely 

 known under the names of Terehratula hnridens Morton and T. milli- 

 punctata Hall, is among the collections associated with species that are 

 its common associates elsewhere. It is found to possess comparatively 

 strong dental i)lates extending the lull length of the ventral beak, and 

 also a retlexed loop extending farther forward than the middle of the 

 shell. The exact (letails of the loop have not yet been nuide out ; but I 

 have at present but little doubt that the shell in question belongs to 

 genus ]Jieh(,snia King. 



CONCUIFEKA. 



Genus Aviculopecten McCoy. 



AvicULOPECTEN CoREYANA (sjj. Hov.) — Shell moderately large; width 

 not exceeding, or a little less than, the height ; margin of the basal half 

 forming almost a true semicircle; posterior margin thence continued 

 straight and parallel with the axis of the shell about half-way to the 

 cardinal margin, then curving outward, it forms with the last-named 

 margin a somewhat acute angle. Hinge-line a little longer than the 

 full width of the shell, at right angles with its vertical axis, projecting 

 farther backward than the posterior border, but not reaching (luite so 

 far forward as the anterior border. 



Left valve (ionvex, most so in the umbonal region ; beak prominent, 

 not projecting beyond the cardinal border; posterior ear moderately 

 large, acutely angndar at the outer extremity, not distinctly defined from 

 the body of the valve; anterior ear defined by a moderately deep byssal 

 sinus and a distinct depression running from it to the beak, not so prom- 

 inent as the other ; its outer border rounding downward and inward 

 from the cardinal border into the byssal sinus, where it is met bs' the 

 incurving anterior border of the body of the valve. 



Surface marked by numerous fine, radiating cost;e of unequal size, 

 which are in turn marked by very fine radiating strije, all crossed by 

 fine, concentric lines of growth and occasional coarser lines of increment. 

 Upon the posterior ear, the radiating costie are obsolete ; but upon the 



