SWALLOW — DESCRIPTION OP NEW FOSSILS. 95 



small, rounded at the extremities; surface smooth, punctate, 

 with a few concentric lamellae of growth near the margins, 

 and a i'cw short depressed spines near the borders. Inner 

 surface marked with a double plication from the umbo down 

 the middle, and an obsolete fold on each side. Dorsal valve 

 not seen. 



Length, .56; width, .00 ; height, .23. 



This very rare fossil was obtained from the 3d Archimedes 

 Limestone at Barrett's Station, St. Louis county, Missouri. 



Allorisma antiqua. 



Shell small, symmetrical and finely plicated; beaks promi- 

 nent, incurved, contiguous ; cardinal margin straight or con- 

 cave ; anterior margin slopes abruptly from the beaks to the 

 end below the middle, whence it curves regularly to the ven- 

 tral margin, which is slightly convex, curved abruptly to the 

 posterior extremity above the middle ; valves convex on the 

 anterior and middle portions, compressed towards the pos- 

 terior extremity and ventral margin, with a wide shallow 

 sinus from the beak to the ventral margin. Surface marked 

 with small concentric plications. 



Length, 1.40; width, .77; thickness, .48. 



This species is very much like the A. regulare of Prof. King ; 

 but it is much smaller, and the regulare has no sinus on the 

 sides of the valves. 



This shell is common in the Kaskaskia Limestone in Illi- 

 nois and Missouri. 



Cypricardia(?) Pikensis. 



Shell transverse, ovate, plicate ; beaks high, incurved, ap- 

 proximate, near the anterior end ; cardinal margin curved 

 down at each end ; ventral margin convex, most abuptly 

 curved towards the anterior extremity ; anterior cardinal 

 margin convex, and slopes abruptly to the extremity below 

 the middle ; posterior end narrower, regularly rounded ; 

 valves flattened towards the margins ; surface marked with 

 broad concentric folds. 



Length, 1.36; height, 1.00; thickness, .61. 



This fossil is rare in the Coal Measures of Pike county, 

 Missouri, where it was discovered by Mr. Broadhead. 



CYPRICARDIA(?) SllCMARDIANA. 



Shell small, ovate, plicate ; beaks small nearer the anterior 

 end, incurved, approximate ; cardinal margin convex behind 

 the beaks and concave before them ; anterior end narrower, 

 subacute, rounded from the extremity (which is above the 



