316 BRANSOX AND GREGER ^AMSDEX FORMATION OF WYOMING 



are too poorly preserved to show whether there were fine spines on the 

 concentric raised lines, and the concentric lines are indistinct on most of 

 the exfoliated surfaces. The measurements of the specimen figured are: 

 Length, 23 millimeters; greatest breadth, 27 millimeters. 



MEEKELLA AMSDENEX8IS n. sp. 

 Plate 18, figures 22-25 



Shell slightly smaller than in M. striatocostata, longer than broad, the 

 greatest width near the anterior margin. Length from umbonal region 

 to front margin, 25 millimeters ; greatest breadth, 23 millimeters ; thick- 

 ness, 17 millimeters. 



Pedicle valve convex, with umbo prominent, eccentric, flattened. Car- 

 dinal area narrow and high, relation about 16 to 9, with the delthyrium 

 occupying about one-fourth of the area. Surface marked by numerous 

 minute cost^, subequal in size, separated by slightly wider interspaces, 

 and increasing toward the margin, in the main by intercalation, but also 

 by bifurcation. About three costse to the millimeter. 



Brachial valve more convex than the pedicle, subcircular, strongest 

 slope toward the hinge line. Surface marked by costse similar to those 

 on the pedicle valve. 



Internally the pedicle valve bears two parallel dental plates, about one 

 millimeter apart, which extend forward about half the length of the valve. 



This is the first Meekella reported from below the Pennsylvanian in 

 America and, like the Lower Carboniferous Meekellas of England, it 

 lacks plications.'^ 



SPIRIFERINA BROWXI n. sp. 

 Plate 18, figm-es 15 and 17 



Shell below medium size ; broader than long ; the greatest width a short 

 distance in front of the hinge line; cardinal extremities rounded. The 

 dimensions of a nearly perfect specimen of medium size are : Length, 15 

 millimeters; breadth, 18 millimeters; thickness, 10.5 millimeters; height 

 of cardinal area, 2.4 millimeters. 



Pedicle valve strongly convex, most prominent in the umbonal region; 

 each lateral slope marked by 6 to 7 rounded to subangular plications. 

 Mesial sinus sharply defined, rounded; beaks small, slightly incurved; 

 cardinal area well developed, concave; delthyrium as wide as high. In- 

 ternally a stro]ig meflian septum reaches half the length of the valve, and 

 the dental plates are about half the length of the median septum. 



■^ Memoirs of the Geological Survey of Great Britain. I'aleontology, vol. 1, part 2, pp. 

 112-114, pi. 13, figs. 1, 2.. 



