20 Trans. Acad. Sci. of St. Louis. 



Syringothyris cakteri (Hall). 



PL IV. f. 5,6. 



Shell subsemielliptical in outline, the width about three- 

 fourths greater than the length, the cardinal extremities 

 usually nearly rectangular. The brachial valve convex, some- 

 times becoming gibbous, the beak incurved, the mesial fold 

 regularly rounded without plications. Pedicle valve sub- 

 conical in form, the mesial sinus well defined, the cardinal 

 area arched, its height about two-fifths the breadth of the 

 shell, the delthyrium large, the sides forming an angle of 

 about 38 degrees. Surface of each valve marked by about 

 fifteen simple, rounded plications on each side of the fold and 

 sinus: in the casts, these plications become less and less dis- 

 tinct from the center to the cardinal extremities of the shell, 

 where they become obsolete with still room for three or four 

 additional ones which would probably be distinguishable upon 

 the exterior of a perfectly preserved shell. Besides the pli- 

 cations, the shell is marked by concentric lines of growth, 

 and the area of the pedicle valve by both vertical and trans- 

 verse striae. 



Remarks. Although the characteristic canaliferous plate 

 of Syringothyris has not been observed in the Northview 

 specimens, nor the punctate shell structure, they are placed 

 with little or no hesitation in this genus because of the high 

 cardinal area and the unplicated fold and sinus. Two well 

 preserved specimens of the brachial valve, besides fragments, 

 and one imperfectly preserved ventral valve showing the 

 cardinal area, have been observed, and these agree closely with 

 the original description of S. carteri. 



Ambocoelia parva n, sp. 



PL IV. f. 1-4. 



Shell from 3 to 5 mm. in width. The length a little less 

 than the width, subelliptical or subcircular in general out- 

 line, the hinge-line shorter than the greatest width of the 

 shell. Pedicle valve gibbous with the umbo highly elevated, 

 the beak obtuse and moderately incurved, the cardinal 

 area not sharply defined. Surface smooth except for the 

 sharply impressed, groove-like mesial sinus. Brachial valve 

 unknown. 



