have also been found abundantly on the Sharon horizon, in the black 

 shales overlying the coal and in the ore, and also at one locality 

 in the Boggs member. Average sized individuals from the various 

 horizons in which they occur have the following measurements: 



Sharon Quakertown Bear Run Boggs 



Length 15 mm. 9 mm. 15.5 mm. 16.2 mm. 18.5 mm. 



Height 8.5 mm. 5.5 mm. 9.5 mm. 9.7 mm. 9.5 mm. 



Thickness 3.8 mm. 



The members of this genus, as they are found in Ohio, occur either 

 wholly by themselves, or associated with plant remains and fish scales. 

 However, a few poorly preserved specimens of a large obscure species 

 of Naidites are found with large numbers of Lingula carbonaria on 

 the Anthony coal horizon. Often N.elongata is so abundant that a 

 freshly broken surface of shale presents a mass of crushed and macerated 

 individuals. 



Horizon and locality. Sharon horizon: Harry Odle mine, Scioto 

 County (Locality 4), r; John Alexander mine, Scioto County (Locality 

 3), c. Quakertown or No. 2 Coal horizon: Grace mine, Twin-Ada 

 mine, and Wilson mine, Muskingum County (Localities 11, 10, 9), r. 

 Bear Run horizon: abundant in Scioto, Jackson, and Vinton counties 

 in all localities from which collections were made (Localities 13, 14, 

 15, 16, 17, 18). Boggs member: Bloom Township, Scioto County 

 (Locality 23), a. 



Naiadites ohionese n.sp. 

 PI. IV, Figs. 25, 26, 27. 



Description. Shell small, obliquely elongate, gibbous, the greatest 

 thickness being a little anterior to the middle, right valve a little 

 more compressed than the left, shell gaping along ventral and posterior 

 margins; hinge line almost or entirely as long as the greatest length 

 of the shell; beaks minute, anterior but not quite terminal, incurved, 

 slightly elevated above the hinge line; anterior lobe small, prominent, 

 gibbous, projecting a little beyond the beak, rounding into the ventral 

 or inferior margin; ventral margin concave in middle, bluntly rounded 

 posteriorly; posterior portion of shell forming the greatest height of 

 the shell, margin straight or very slightly rounded, meeting the hinge 

 line at an angle which is either a little greater than or equal to a right 

 angle; a prominent, gibbous umbonal ridge extending obliquely back- 

 ward from the beak to the posterior-inferior angle, broadening poster- 

 iorly, but preserving its distinctive character throughout its extent; 

 a deep, oblique sinus anterior to the ridge, separating the anterior 

 lobe from the remainder of the shell; region below hinge line depressed. 

 Surface marked by fine, regular, concentric lines of growth. 



Dimensions. A cotype measures: Maximum length 12 mm., 

 maximum height near posterior margin 8 mm., length of hinge line 

 9.5 mm., convexity 6.5 mm. 



74 



