SWALLOW — DESCRIPTION OF NEW FOSSILS. 99 



form, exhibiting all the volutions ; suture, on the inside, dis- 

 tinct and impressed; aperture oblique, subangular. Surface 

 marked with unequal transverse rugae and fine striae. 



Diameter of base, .79; height of spire, .48; diameter of 

 aperture, .30. 



This fossil is abundant, in some localities, in the 1st Ar- 

 chimedes or Kaskaskia Limestone. 



EUOMPHALUS BoONENSIS. 



Shell small, plano-concave ; whorls three or four, carinated 

 on the junction of the upper and outer margins ; from which 

 the outer surface is convex ; thence flattened and sloping in 

 to a subcarinated edge on the lower margin ; convex from 

 the lower edge to the suture ; upper surface from the carina 

 to the suture slightly convex : suture on each side impressed 

 and conspicuous ; aperture subangular. Surface marked with 

 transverse striae parallel to the periphery of the aperture. 



Diameter, .90 ; diameter of aperture, .33. 



This shell most resembles the E. latus of Prof. Hall ; but 

 its size and the shape of the volutions make it very distinct. 



It is a rare fossil in the Encrinital Limestone of Missouri. 



Dentalium Missouriense. 



Shell of medium size, thin, terete, subarcuate, inflated at 

 the aperture. Surface marked with small, distant, longitudi- 

 nal costas. 



Length from two to three inches. 



Very rare in the upper divisions of the Archimedes Lime- 

 stone at Chester, Illinois, and St. Mary's, Missouri. 



Pleubotomaria(?) Chesterensis. 



Shell small, oblique, conical : whorls, five or six veiy con- 

 vex ; last whorl much larger, expanded towards the aperture; 

 flattened on the outer margin with a larger and deeper sulca- 

 tum on each side of the flat band : aperture oblique, orbicular, 

 or ovate : suture distinct and deeply impressed. Surface 

 marked with small, rounded, revolving costae. 



Length, .75; width of base, .47; length of aperture, .30. 

 Spire above the last whorl more than half the length of the 

 shell. 



This fossil is rare in the Upper Archimedes Limestone at 

 Chester, Illinois. 



Pleurotomaria trochiformis. 



Shell depressed conical, tapering rapidly. Volutions flat- 

 tened on the outer and upper side, obtusely carinated on the 



