DESCRIPTION OF SPECIES 191 



ences render such identification doubtful. The Lowellville form is 

 small, about one-half the size of A. planoconvexa, narrower, with a 

 shorter hinge line which equals only about one-half the greatest width 

 of the shell. The beak of the ventral valve is somewhat broader and 

 less elevated; it is marked by a faint, narrow sinus which becomes 

 evident near the beak. However, occasionally specimens of A. plano- 

 convexa are found on which the differences mentioned above are not 

 very evident, so that a new specific or even a new variety name for the 

 Lowellville form may not be justifiable, especially as the material at 

 hand is not in first-class condition. 



Dimensions. A large ventral valve measures: length 4.5 mm., 

 width 5.5 mm., convexity 2.2 mm. A dorsal valve of average size 

 measures: length 2.2 mm., width 2.7 mm. 



Horizon and locality. Lowellville member: Poverty Run, Mus- 

 kingum County, Locality 19, c. 



Genus Squamularia Gemmellaro 

 i 



Squamularia perplexa (McChesney) 



* 



PI. IX, figs. 26, 27 



1856 Spirifer lineatus. Hall, Pac. R. R. Rep., Vol. 3, p. 101, PI. 2, Figs. 6-8. 



(Non S. lineatus Martin, 1809.) 



Carboniferous: Pecos Village, New Mexico. 

 1860 Spirifer perplexa. McChesney, Desc. New Pal. Foss., p. 43. 



Upper Coal Measures: Almost every part of the country where rocks of 



that age occur. 

 1899 Reticularia perplexa. Girty, U. S. Geol. Surv., Nineteenth Ann. Rept., Pt. 3, 



p. 577, PI. 72, Fig. la. 



Upper Coal Measures: McAlester quadrangle, Indian Territory. 

 1903 Squamularia perplexa. Girty, Prof. Paper, U. S. Geol. Surv., No. 16, p. 392, 



PI. 6, Figs. 8-1 Ic. 



Humerosa, Weber, and Maroon formations: Colorado. 



Description. This is an abundant and widely distributed fossil 

 in the marine limestones of the Pottsville formation above the Boggs 

 member, although it is rare in the latter horizon. It occurs as a rule 

 as internal casts on which fine concentric bands of spines or traces of 

 them are usually visible. The Ohio specimens are somewhat larger 

 than those described by McChesney which seldom attain a width of 

 more than five-eighths of an inch. 



Dimensions. A specimen of average size from the Lower Mercer 

 limestone measures: length 16 mm., width 19.5 mm., convexity 5 mm. 



Horizon and locality. Bog-gs limestone: Symmes Creek, Mus- 

 kingum County, Locality 29, r. Widely distributed throughout the 

 Lower Mercer, Upper Mercer, McArthur, and Black Flint members, a. 



