408 MISSISSIPPIAN BRACHIOPODA 



Remarks. This species has been described in the main from specimens 

 from the white cherts of Lower Burlington age, from Louisiana, Missouri. 

 None of the specimens, from this locality, which have been studied are com- 

 plete, but they preserve all of the essential characters and exhibit the fine 

 surface markings in a most perfect manner. Several specimens from a 

 similar horizon at Osceola, Missouri, are somewhat larger, the largest 

 one having a width along the hinge-line of about 60 mm., but they agree 

 with the Louisiana specimens in all essentials except in having a larger 

 number of plications, there being 20 or more upon each lateral slope, a 

 character doubtless due to the larger size of the individuals. The species 

 differs from S. gigas in its smaller size, its greater angle between the car- 

 dinal area and the plane of the valve, and in the more rounded lateral 

 margins of the area. 



The shell illustrated by Keyes as Syringothyris carteri is certainly a 

 member of this species, although it is proportionally somewhat wider 

 along the hinge-line and consequently has a relatively lower cardinal area. 

 It has the rounded lateral margins of the cardinal area of this species and 

 closely resembles none of the species of SyringotJiyris. 



Horizon. Burlington limestone. 



PSEUDOSYRINX KEOKUK n. Sp. 



Plate LXVI, Figs. 6-10 ; Plate LXVII, Figs. 1-9 



Description. Shell of about medium size, broader than long, the great- 

 est width near the hinge-line, the cardinal extremities rounded. The 

 dimensions of a nearly complete internal cast are : length of pedicle valve 

 from beak to front margin 17 mm., length of brachial valve 15 mm., 

 width 28 mm., length of hinge-line 22.5 mm., thickness 41.1 mm., height 

 of cardinal area 9.8 mm., width of sinus in front 9.5 mm., width of delthy- 

 rium at hinge-line 5.4 mm. 



Pedicle valve subpyramidal in form, the surface sloping in nearly 

 straight lines from the beak to the lateral extremities and with a gently 

 convex curvature to the antero-lateral and anterior margins ; mesial sinus 

 of moderate depth, rounded in the bottom, narrow and well defined at the 

 beak, becoming broader and less sharply defined anteriorly, produced in 

 front in a rounded lingual extension ; beak small, pointed, a little curved ; 

 cardinal area nearly flat below, becoming gently concave towards the 

 apex just under the beak, sloping anteriorly from the hinge-line at an 

 angle of about 55 degrees to the plane of the valve, its lateral mar- 

 gins rounding regularly into the surface of the lateral slopes of the 

 valve, the vertically marked, differentiated, triangular region lying on 

 either side of the delthyrium has a width along the base of the triangle 

 about equal to one-half the length of the hinge-line ; delthyrium narrowly 

 triangular, the width at the base about one-half the height; each lateral 



