100 TRANS. OP THE ACAD. OF SCIENCE. 



outer margin ; the last one convex below ; the others, at their 

 base projecting beyond the top of the one below : umbilicus 

 deep, infundibulitbnn : aperture angular. Surface marked 

 with sharp, distinct, transverse striae, parallel to the margin of 

 the aperture. 



This shell resembles the P. Woriheni of Prof. Hall ; but its 

 spire is larger, more conical, has no revolving costse on the 

 lower side of the body whorl, and the lower part of the upper 

 volutions do not project so much in the Woriheni. 



Dr. Giddings collected this fossil from the Archimedes 

 Limestone of Cooper county, Missouri. 



Bellerophon Missouriensis. 



Shell subglobose ; outer whorl carinated, inflated at the aper- 

 ture ; aperture very large, transverse, sinuate in front. Surface 

 marked with small, rounded, longitudinal costae and trans- 

 verse striae parallel to the aperture. 



This fossil is common in the upper beds of the Archimedes 

 Limestone, at Chester, Illinois. 



Natica Ciiesterensis. 



Shell of medium size, ellipsoidal, oblique ; spire small, de- 

 pressed ; volutions five or six, convex ; suture depressed and 

 filled with enamel ; body whorl large and convex ; aperture 

 oblique, elliptical; anterior extremity somewhat prolonged 

 and slightly reflected. Surface is marked with numerous, 

 minute, thick-set, oblique papillae. 



Length, 1.00; length of spire, .35 ; diameter of body whorl, 

 .60 ; length of aperture, .60 ; breadth of aperture, .50. 



This fossil is rare in the 1st Archimedes or Kaskas- 

 kia Limestone at Chester, Illinois, and near Ste. Genevieve, 

 Missouri. 



Macrociieilus Cooperensis. 



Shell small, obliquely conical ; whorls four or five, very con- 

 vex, the last very large ; spire one half the length of the 

 shell, tapering rapidly; last whorl very large, most convex 

 near the lower margin, subflattened on the upper and outer 

 margin ; suture deeply impressed. 



Length, .47; diameter of base, .30; length of aperture, .25. 



This fossil was discovered in the Archimedes Limestone of 

 Cooper county, by Dr. Giddings. 



