334 Systematic Paleontology 



region. The brachial valve is always very convex. Marginal outline of 

 the valve subcircular. On the pedicle valve the hinge-line is straight but 

 short, the cardinal area low, and the beak retrorse. The delthyrium is 

 broad, and covered by an imperforate convex deltidium. The teeth are 

 moderately large and are supported by lamellae which extend to the bottom 

 of the umbonal cavity, and are produced into strong ridges entirely sur- 

 rounding the muscular area. This area is very large, having the struct- 

 ure of that in extreme examples of Ehipidomella, such as Ortliis muscu- 

 losa, and is composed of broad, flabellate diductors enclosing an elongate 

 or cordate adductor impression. There is a low median septum in the 

 umbonal cavity, separating the arms of the cardinal process of the opposite 

 valve, but it is quite short, disappearing at the adductor scar, though 

 sometimes reappearing in front of it. 



" In the brachial valve there is no cardinal area. Tlie cardinal process 

 has essentially the same structure as in Orthothetes [ = Schuchertella] 

 and Derbya [ = Orthotetes], but is very high, its two branches completely 

 traversing the umbonal cavity of the opposite valve; it is supported by a 

 short, median septum, and laterally by strong crural plates -which extend 

 for a short distance along the margins of the muscular impressions ; these 

 are usually quite faint and undefined, occupying a much smaller area than 

 in the pedicle valve, and leaving arborescent markings as in some species 

 of Stropheodonta. On the interior of both valves the margin is sharply 

 pectinated, or crenulated, the cronulations on the brachial valve extending 

 to the base of the cardinal process, and in the pedicle valve extending for 

 a considerable distance on the cardinal area. Surface 'of both valves 

 covered with fine sharp radiating striae." Hall and Clarke, 1892. 



Length about 3 cm. ; width abont 4 cm. 



This well-known and widely distributed brachiopod is not common in 

 the Upper Oriskany of Maryland, nor does it attain the large size of New 

 York examples. 



Occurrence. — Oriskany Formation, Ridgely MembI':r. Devil's Back- 

 bone, Knobly Mountain near Cumberland, Maryland; Pendleton County, 

 West Virginia. 



Collection. — U. S. National Museum. 



