DESCRIPTION OF SPECIES BRACHIOPODA 295 



RHIPIDOMELLA MICHELINIA L'Eveille 



Plate 12, figures 8-10 



1835. Orthis michelinia L'Eveille, Memoires de la Societe Geologique de France, 



volume 2, page 39, plate 2, figures 14-17. 

 1858. Orthis michelini var. burlingtonensis Hall, Geology of Iowa, volume 1, 



part 2, page 596, plate 12, figures 4a-b. 

 1858. Orthis michelinia Davidson, British Fossil Brachiopoda, volume 2, page 



132, plate 30, figures 6-12. 

 1892. Orthis (Rhiphlomella) burlingtonensis Hall & Clarke, Paleontology of 



New York, volume 8, part 1, plate 6A, figure 13 ; plate 20, figures 5-6. 

 1894. Orthis burlingtonensis Keyes, Missouri Geological Survey, volume 5, page 



63, plate 38, figure 7. 

 1899. Rhipiclomella burlingtonensis Weller, Transactions of the Saint Louis 



Academy of Science, volume 9, page 15, plate 4, figure 13. 

 1901. Rhipiclomella hurlingtonensis Weller, Transactions of the Saint Louis 



Academy of Science, volume 11, pages 150 and 181, plate 12, figure 3, 



and plate 16, figure 6. 



Description. — Shell lenticular in form, subcircular or subovate in out- 

 line, as wide as or a little wider than long, the greatest width at or in 

 front of the middle, hinge line short, one-third or less than one-third the 

 width of the shell. Pedicle valve depressed convex, most prominent on 

 the umbo, the surface sloping rather abruptly to the cardinal margin 

 with a slightly concave curvature, and gently to the lateral and anterior 

 margins with a moderately convex curvature; the median portion of the 

 valve either not differentiated from the lateral surfaces or flattened or 

 slightly depressed in a broad, shallow, ill defined sinus in the anterior 

 half; in the posterior half of the valve the median portion is somewhat 

 marked by a slight, ill defined median elevation; cardinal area small, a 

 little concave, the delthyrium rather broad. Brachial valve with a con- 

 vexity about equaling that of the pedicle valve ; convexity nearly uniform, 

 but sloping a little more abruptly to the cardinal margins, the median 

 portion of the valve depressed in a rather broad, shallow, ill defined sinus 

 which extends nearly or quite to the beak. Surface of both valves 

 marked by fine, rounded, radiating costse, which increase by bifurcation 

 and intercalation, about two or three costse occupying the space of one 

 millimeter; the surface also marked by concentric lines of growth which 

 vary in strength and distribution in different individuals. 



The dimensions of one of the most complete individuals observed in 

 the Fern Glen fauna are: Length, 20 millimeters; width, 20.5 milli- 

 meters; thickness, 9 millimeters. 



Remarks. — This is one of the most abundant species in the Fern Glen 

 fauna, but it is of smaller size than usual for the species. A length of 



