BRADLEY: HUACHIOI'OPA OK THE MAQ1 < >K l-.'l \ OF Io\\\. 513 



Dinofihis i>r<>tirii<i at Clermont, probably the most common specie , 



i- -mailer than most, of (lie Other Orthidae. 



Locality: — Common in the upper portion of the Maquoketa at 

 Spring Valley, Minnesota and Wilmington, Illinois; Lower Maquo- 

 keta at Clermont, Iowa. M. C. Z. 8,538. 



Strophomenidae. 



Plectambonites rugosis (Meek). 



Leptaena rugosa James, Cat. fossils Cincinnati group, 1871. 



Leptaena sericea var. rugosa Meek, Pal. Ohio, 1873, 1, pt. 2, pi. 5, fig. 3f, g, h. 



Plectambonites rugosa Foerste, Bull. sci. lab. Denison univ., 1912, 17, p. 123, 



pi. 1, fig. 7a-e; pi. 10, fig. 7a-d. 

 Leptae?ia aspera James, Cine, quart, journ. sci., 1874, 1, p. 151. 

 ? 'Plectambonites sericeus var. Ruedemann, Bull. 49, N. Y. state mus., 1901, 



p. 18, pi. 1, fig. 6, 7; ibid., 8, p. 525. 



The typical specimens of this species were found in the Eden at 

 Cincinnati, Ohio. The name rugosa was applied because of the 

 roughened exterior surface and the oblique wrinkles along the hinge- 

 line. 



The concentric banding and filming is often absent as well as the 

 consequent thickening of the valves anteriorly. This is the case with 

 most of the specimens from the Maquoketa near Clermont, Iowa; 

 the surface is comparatively smooth except for concentric striae 

 present on some forms. 



Plectambonites rugosus has a considerable vertical range; it is most 

 abundant in the Eden, but similar forms have been found in the 

 \Yaynesville and Liberty members of the Richmond. Much varia- 

 tion of outline occurs within the species, and on the same slab examples 

 may be seen representing all stages between the semielliptical and the 

 elongate quadrangular. These shells grow more in width than 

 length, and environment often differentiates them so greatly as to 



