DESCRIPTION OF SPECIES BRACHIOPODA 293 



1859. Strophomena rhom'boidalis var. analoga Davidson, British Fossil Brach- 



iopoda, volume 2, page 119, plate 28, figures 1-2. 

 1877. Strophomena rhom'boidalis White, U. S. Geographic Survey West of the 



100th Meridian, volume 4, page 85, plate 5, figure 5. 

 1877. Strophomena rhom'boidalis Hall & Whitf., U. S. Geological Explorations 



of the 40th Parallel, volume 4, page 253, plate 4, figure 4. 

 1888. Strophomena rhomboidalis Herrick, Bulletin of the Dennison University, 



volume 4, plate 9, figure 6. 

 3889. Strophomena rhomboidalis Herrick, American Geologist, volume 3, plate 



4, figure 6. 



1892. Leptcena rhomboidalis Hall & Clarke, Introduction to the Study of the 



Brachiopoda, part 1, plate 13, figure 9. 

 1892. Leptcena rhomboidalis Hall & Clarke, Paleontology of New York, volume 



8, part 1, plate 8, figures 30-31 ; plate 20, figure 24. 



1894. Plectambonites rhomboidalis Keyes, Missouri Geological Survey, volume 



5, page 70, plate 39, figure 0. 



1895. Strophomena rhomboidalis Herrick, Geological Survey of Ohio, volume 7, 



plate 20, figure 6. 



Description. — Shell transversely subsemicircular or subquadrate in 

 outline, the hinge line straight, equaling the greatest width of the shell, 

 the valves geniculate anteriorly and laterally. Pedicle valve slightly con- 

 vex near the beak ; beyond the convex area it becomes flattened to the line 

 of geniculation, where it is abruptly bent toward the opposite valve at 

 nearly a right angle ; on the flattened portion of the valve there are pres- 

 ent a variable number of concentric undulations or wrinkles which are 

 sometimes discontinuous and which bend outward toward the cardinal 

 extremities as they approach the cardinal margin; beak small, not in- 

 curved, with a minute perforation which is sometimes obsolete or ob- 

 scure; cardinal area rather narrow, with a wide delthyrium which is 

 nearly closed by the cardinal process of the opposite valve when the 

 two valves are in articulation, the deltidium being very small and re- 

 stricted to the apex of the delthyrium. Brachial valve concave, the pos- 

 terior portion flattened, bent abruptly upward toward the margin to 

 conform with the pedicle valve; flattened portion of the valve marked by 

 concentric wrinkles or undulations similar to those of the pedicle valve, 

 the cardinal area narrower than that of the pedicle valve. Both valves 

 marked, in addition to the concentric wrinkles, with very fine radiating 

 stria?. 



The dimensions of a specimen of average size are: Length, 20 milli- 

 meters ; width, 28 millimeters. 



Remarks. — This is a rather common member of the Fern Glen fauna 

 and does not differ essentially from members of this long range species 

 from other horizons and localities. 



