48 MISSISSIPPIAN BRACHIOPODA 



Brachial valve depressed conical, the apex situated a little eccentric- 

 ally towards the posterior margin and inclined posteriorly, the surface 

 sloping with a gently convex curvature from the apex to the lateral and 

 anterior margins, becoming a little concave to the posterior margin. In- 

 ternally the adductor muscular scars are well defined, the anterior pair 

 rather close together, situated one at each side of the apex of the valve, 

 the posterior pair somewhat larger than the anterior, marginal in position, 

 much farther apart than the posterior, the distance from center to center 

 being considerably greater than their distance from the anterior scars. 

 External surface of the valve marked by rather obscure concentric lines 

 of growth, and entirely covered by minute, crowded papillae which may 

 indicate the presence of minute, appressed spines upon the living shell. 



Remarks. The name Icevis, given to this species by Keyes, suggests a 

 smooth shell, but the specimen here described and illustrated, which was 

 one of the original types, is clearly papillose when examined under a lens, 

 although it does appear almost smooth to the unaided eye. The specimen 

 is a silicified one, and it is possible that the author of the species mistook 

 these minute papillae for irregularities of the surface due to the silicifica- 

 tion of the shell. The species was originally recorded from the Chouteau 

 and Burlington limestones at Louisiana, Mo., so that the co-types must 

 have been at least two in number, although neither of them were illus- 

 trated. The specimen here figured is the Burlington limestone specimen 

 used by Keyes, now preserved in the collection of Prof. R. R. Rowley at 

 Louisiana. No other example has been observed. The species differs 

 from C. spiculata of the Louisiana limestone in its less circular outline, 

 the more eccentric apex, and the finer surface papillae. 



Horizon. Burlington limestone. 



Order PROTEEMATA 



Family STROPHOMENIM] 



Genus LEFT JEN A Dalman 



Description. Shell plano-convex in youth, becoming normally con- 

 cavo-convex at maturity, transversely subtrapezoidal or semielliptical in 

 outline, hinge-line straight, its length usually' the greatest width of the 

 shell, the cardinal extremities often subauriculate. Pedicle valve with a 

 narrow cardinal area, the delthyrium closed by a convex deltidium, per- 

 forated at the apex of the beak by a foramen which is commonly filled at 

 maturity. Brachial valve with a cardinal area narrower than that of the 

 pedicle valve, the cardinal process large and bifid, surrounded posteriorly 

 by a well-developed chilidium. The surface of both valves marked pos- 

 teriorly by conspicuous concentric corrugations and where these cease 



