4 mm; one of the average size from the Lower Mercer limestone: 

 length 9 mm., width 18.5 mm. 



Horizon and locality. Harrison ore: Jackson County (Locality 1), 

 c. Sharon ore: Lick Run, Scioto County (Locality 2), c. Lowellville 

 and Boggs members: generally distributed, r. Universal in distribu- 

 tion and common in the Lower Mercer and higher members of the 

 Pottsville formation. 



Genus Spirifer Sowerby 



Spirifer boonensis Swallow? 



PI. Ill, Figs. 13, 14, 15, 16. 



1860 Spirifer boonensis. Swallow, Trans. St. Louis Acad. Sci., Vol. 1, p. 646. 



Lower Coal Measures: Boone, Randolph, and Monroe counties, Missouri. 

 1903 Spirifer boonesis ? Girty, Prof. Paper, U. S. Geol. Surv... No. 16, p. 381, PL 6, 



Figs. 1-3. 



Carboniferous: Colorado. 



Description. Shell large, subquadrate in outline, convex, ratio 

 length to width about 2.3; hinge line produced, always forming the 

 greatest width of the shell. Ventral valve strongly convex, beak 

 highly elevated and incurved over the hinge line; cardinal area, broad, 

 transversely striated; delthyrium large; mesial sinus well defined, 

 becoming broad and deep toward the front, always marked by at least 

 three strong, rounded ribs, but sometimes by five ribs, the lateral 

 one on each side in the latter case being smaller and formed by the 

 bifurcation of the ribs bounding the sinus. Dorsal valve less convex 

 than the ventral, beak incurved and slightly elevated above the hinge 

 line; mesial fold strongly elevated, consisting of four to six ribs, the two 

 middle ones extending to the beak but bifurcating posterior to the 

 middle of the valve, so that four plications always reach the front; 

 two smaller, lateral plications sometimes originating by the further 

 bifurcation of the outer ribs. Surface on either side of the fold and 

 sinus marked by ten to twelve simple, rounded ribs which are covered 

 with fine, radiating lines; crossed by a few faint concentric lines of 

 growth near the front and lateral margins. 



Dimensions. The following measurements were made of four 

 large specimens, two of which are ventral valves, and two, dorsal 

 valves: 



Ventral valves Dorsal valves 



Length of hinge line (maximum 



width) . . , 37 mm. 33 mm.; 41 mm. 35 mm. 



Length of shell .20 mm. 19 mm.; 28 mm. 23 mm. 



Convexity 4.5 mm. 4.5 mm.; 7 mm. 5.5 mm. 



Remarks. This species is common throughout the marine lime- 

 stones of the Pottsville formation of this State including and above 

 the Boggs member, but is especially abundant in the Boggs, Lower 

 Mercer, and McArthur limestones. It appears identical with the 



56 



