390 MISSISSIPPIAN BRACHIOPODA 



The minute surface markings of the shell consist of concentric series 

 of exceedingly fine and narrow, subrhomboidal depressions which are 

 deeper at their proximal or posterior extremities, these depressions being 

 arranged alternately in succeeding rows. Eather strong concentric lines 

 of growth are present upon all non-exfoliated specimens, which are of 

 varying degrees of strength and are irregularly distributed from the 

 beak to the front. Shell structure punctate. 



Remarks. This is one of the forms which Schuchert has made synony- 

 mous with 8. carteri, but it is undoubtedly a well characterized species, and 

 so far as known is confined to the fauna of the Louisiana limestone. 



Horizon. Louisiana limestone of the Kinderhook. 



SYRINGOTHYRIS HALLI Winchell 

 Plate LXXII, Figs. 13-23 



1863. Syringothyris Haiti Winchell, Proc. Acad. Nat. Sci. Phil., p. 8. 

 1901. Syringothyris halli Weller, Trans. St. Louis Acad. Sci., vol. 11, 

 p. 158, pi. 13, figs. 1-3. 



Description. Shell below medium size, much broader than long, the 

 greatest width along the hinge-line, the cardinal extremities acutely 

 angular. The dimensions of a nearly complete example are : length of 

 pedicle valve from beak to front margin 12.8 mm., length of brachial 

 valve 12.2 mm., height of cardinal area 10.9 mm., width along hinge-line 

 30.6 mm., thickness 13 mm., width of sinus in front 7.2 mm. 



Pedicle valve subpyramidal in form, the surface sloping from the 

 beak to the cardinal extremities and to the anterior margin in nearly 

 straight lines or with but slight curvature; the mesial sinus of mod- 

 erate depth, rounded in the bottom, rather sharply defined through- 

 out, originating at the beak and increasing in width regularly to 

 the front, produced anteriorly in a rather short, rounded, lingual exten- 

 sion ; beak pointed, erect, or very slightly incurved ; cardinal area high, 

 sloping posteriorly from the hinge-line at an angle of from 50 to 60 de- 

 grees to the plane of the valve, broadly triangular in outline, flat or 

 slightly concave, the lateral margins sharply defined; delthyrium nar- 

 rowly triangular, the height about one and one-half the width ; each lateral 

 slope bearing about 16 simple, depressed plications which originate along 

 the cardinal margin and grow successively finer towards the cardinal 

 extremities. Internally the dental lamellae are well developed, diverging 

 from the beak at a wider angle than the sides of the mesial sinus, and 

 extending nearly one-half the length of the shell from the beak to the 

 front margin on each side of the sinus ; the transverse plate between the 

 dental lamellae reaches less than half way from the beak to the hinge-line, 

 its external surface is marked by a distinct, longitudinal, median ridge 



