180 MISSISSIPPIAN BRACHIOPODA 



of the mesial fold ; the beak strongly incurved beneath that of the oppo- 

 site valve; the plications similar in form and number to those of the 

 opposite valve and alternate with them, the concentric markings also 

 similar to those of the opposite valve. 



Remarks. This is a small species which was originally described from 

 New Mexico and the above description has been drawn up from speci- 

 mens collected at the type locality. Examples of the same species seem 

 to be present in the Chouteau limestone of Missouri and Illinois, at least 

 no characters have been detected which seem to be of sufficient import- 

 ance to differentiate the two forms, although the Chouteau limestone 

 examples seem to be somewhat more rotund and have slightly less angular 

 plications anteriorly in the sinus. 



Horizon. Chouteau limestone and lower Burlington limestone. 



CAMAROTCECHIA SUBLOGOSA n. sp. 

 Plate XXIV, Figs. 29-33 



Description.- Shell small, subglobose in form, the outline subovate, the 

 length greater than the width, the greatest width near the mid-length of 

 the shell. The dimensions of a nearly perfect internal cast are : length 

 of pedicle valve 12.5 mm., length of brachial valve 10.7 mm., greatest 

 width 10.8 mm., thickness 9 mm., width of sinus in front 5.9 mm. 



Pedicle valve strongly convex, the greatest convexity near the middle, 

 the surface curving abruptly to the postero-lateral margins, less abruptly 

 to the antero-lateral and more gently to the anterior margin ; mesial sinus 

 originating near or a little back of the middle of the valve, only slightly 

 depressed below the general surface, nearly flat transversely across the 

 bottom, produced anteriorly in a rather short and broad mesial extension ; 

 beak rather prominent in the internal casts and only moderately in- 

 curved; plications simple, subangular, probably extending to the beak 

 upon the external surface but becoming faint and obsolete towards the 

 beak on the internal cast, three are present in the sinus and seven or eight 

 upon each lateral slope, the last two or three towards the cardinal ex- 

 tremities becoming faint and at last nearly obsolete ; rather crowded, fine, 

 con-centric lines of growth are present upon the internal cast over at least 

 the anterior half of the valve, with an occasional stronger one, and upon 

 the external surface these markings were doubtless strongly developed 

 over the entire surface of the valve. Internally the dental plates are 

 rather strong and of moderate length and between them is a well defined 

 muscle scar which extends anteriorly for about one-third the length of 

 the valve. 



Brachial valve subcircular in outline, but little more convex than the 

 pedicle, its greatest convexity near the middle, the surface describing 



