Horizon and locality. Anthony shales: Scioto Furnace, Scioto 

 County (Locality 8), a. 



Genus Orbiculoidea d'Orbigny 

 Orbiculoidea stoutella n. sp. 

 PL III, Figs. 6, 7, 8 



Description. Shell large for specimens of this genus, subcircular 

 in outline, gibbous, width slightly greater than length. Ventral valve 

 unknown. Dorsal valve with widest portion a little anterior to middle 

 of shell; anterior margin broadly rounded, posterior margin more 

 narrowly rounded; greatest convexity about the middle of the valve; 

 beak small, very inconspicuous and depressed, situated almost at the 

 posterior margin of the shell; area posterior to beak sloping to the 

 margin with a concave outline. Epidermis of shell where preserved, 

 thick, with surface marked by fine, closely arranged, irregular, con- 

 centric lines of growth. 



On the specimens at hand, which are for the most part casts of 

 the interior, not only are internal markings of especial interest retained, 

 but they are preserved in an unusual manner. A well-marked rhombo- 

 hedral or lozenge-shaped visceral area is present in the posterior por- 

 tion, extending anteriorly about one-third or more of the length of 

 the shell. The posterior margin of this area includes the beak and is 

 sharply marked, but is less well defined laterally and anteriorly. The 

 anterior edge of the lozenge-shaped area is bordered by two shallow 

 rather faintly defined grooves, one on either side of a low median 

 septum, which extend diagonally upward toward the lateral angles 

 of the area. These grooves were formed by ridges on the inside of 

 the shell, which doubtlessly served for the attachment of muscles, 

 and apparently correspond to the anterior muscular ridge of Lindstro- 

 emella aspidium as figured by Hall and Clarke. 1 On either side of 

 the median septum and just above the muscular ridge is a sharply 

 defined, large, elevated (therefore deeply impressed on the interior of 

 the shell) muscular scar; while closer to the septum and on either 

 side of it, is an irregular, less well-defined area of muscular attach- 

 ments which probably represent the anterior adductor muscular 

 scars. The writer has been unable to work out the function of the 

 muscles which produced the more laterally placed pair of scars, al- 

 though the possibility exists that they may represent the lateral scars 

 shown in the figure of Lindstroemella aspidium cited above. The 

 median septum is short, extending anteriorly one-half the length 

 of the visceral area, but dying out a little posterior to it. From the 

 two lateral angles a prominent, elevated (on the internal cast) vascular 

 sinus extends obliquely forward to the anterior-lateral margins of 

 the valve; the sides and front of the shell, as well as the region poster- 

 ior to the beak, are .marked by numerous fine, thread-like, radiating, 



'Hall and Clarke, Pal. New York, Vol. 8, Pt. I, PI. 4E, Figs. 25, 26, 1892. 



46 



