MARYLAND GEOLOGICAL SURVEY 233 



division of the Maysville at Cincinnati, Ohio, and vicinity. This species 

 has the subquadrangular outline of Lingula elderi Whitfield from the 

 Black Eiver group of Minnesota and Wisconsin, but its anterior end is 

 more drawn out. It is also closely related to L. rectilateralis Emmons 

 from the Utica shales of New York, but lacks the fine radiating striae of 

 that species, is more elongate and less quadrate. 



Occurrence. MARTINSBURG SHALE (Orthorhynchula bed at the top-of 

 the Fairview division). Head of Eaver's Eun, three and one-half miles 

 southwest of Saxton, Pennsylvania. 



The figured specimens are from the upper part of the Fairview forma- 

 tion at Cincinnati, Ohio. 



Collection. U. S. National Museum. 



. order NEOTREMATA 



Family OBOLELLIDAE 



Genus OBOLELLA Billings 



OBOLELLA MINOR (Walcott) 



Plate XXV, Figs. 1-4 



Camarella minor Walcott, 1890, Proc. U. S. Nat. Mus. for 1889, vol. 12, 



pp. 36-37. 

 Camarella ? minor Walcott, 1891, Tenth Ann. Kept. U. S. Geol. Survey, p. 614, 



pi. Ixxii, figs. 4, 4a-d. 

 Camarella minor Hall and Clarke, 1894, Nat. Hist. New York, Paleontology, 



vol. 8, pt. 2, p. 221. 

 Obolella minor Clark and Mathews, 1906, Maryland Geol. Survey, vol. 6, pt. 1, 



p. 252, pi. xvi, figs. 13 and 14. 



Description. " General form ovate, biconvex. Surface smooth or 

 marked by concentric lines and varices of growth. Ventral valve suba- 

 cuminate, moderately convex, with the most elevated portion at the umbo, 

 which curves toward the small apex ; the posterior or umbonal third of the 

 valve is usually more or less tumid, a ridge of growth separating it from 

 the anterior portion of the shell ; area nearly on the plane of the margins of 

 the valve and divided midway by narrow, deep, pedicle furrow; casts of 

 the interior show that the area formed a shelf on each side of the pedicle 

 furrow. Dorsal valve transversely ovate; a narrow, short area and a 

 slight median ridge are indicated on a cast of the interior. 



