230 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxviii. 



BILLINGSELLA ? ANOMALA, new species. 



Shell sul)([uadrilateral, with the dorsal valve transvei'se. On the 

 ventral valve the cardinal line slopes toward the beak at an angle of 

 from 15° to 20°, while in the dorsal valve it is nearly straight. The 

 greatest width of the valves is about the middle of the shell. Owing 

 to compression and consequent distortion there is considerable varia- 

 tion in the relative proportions of length and breadth. The cardinal 

 angle is acute, in some instances extending out some distance bej^ond 

 the widest portion of the shell, resembling in this respect the cardinal 

 angles of some of the Stromphomenida?. All of the specimens are so 

 compressed in the shale that little is preserved of their natural con- 

 vexit3\ A low, broad, mesial sinus occurs on the dorsal valve, and 

 there is a slight flattening of the anterior central portion of the ven- 

 tral valve. 



The surface is marked by tine, radiating stri;e that are increased in 

 number toward the front by the addition of interstitial stria?, giving 

 a fasciculate appearance to the surface. The radiating striie are 

 crossed by concentric lines of growth and tine striw. The surface as 

 described occurs in one specimen, all other specimens being nearly 

 smooth. This, however, may arise from maceration and flattening 

 out of the surface characters by compression. The interior of the 

 shell appears to have been covered b}" minute punctffi. 



The largest specimen of the collection has a transverse diameter of 

 14 mm. " The average size of the ventral valve is about 8 mm. in 

 height by 8 mm. in width. 



Cardinal area about one-fifth the height of the shell. It is marked 

 by transverse stri* of growth that cross it parallel to its base. 

 Delthyrium rather broad. No traces of the deltidium have been 

 observed. Cardinal area of the dorsal valve short. It is divided 

 midway by a strong delthyrium. Nothing is known of the interior 

 characters except the presence of short crura in the dorsal valve. 



Observations. — This shell occurs quite abundantly in the' very fine, 

 buff-colored, argillaceous shales of the Coosa Valley Cambrian section. 

 There is doubt as to its surface characters, as only one specimen found 

 in the same beds has radiating stride. All others appear to be nearly 

 smooth. Its strongest character is the extension of the cardinal angle. 

 Owing to the imperfection of the material the generic reference is 

 doubtful. 



Formation and locality.- — Middle Cambrian, Coosa Valley shales. 

 Cowan Creek section. Edwards farm, near Craigs Mountain, Chero 

 kee County, Alabama. 



