286 PALEONTOLOGY OF ILLINOIS. 



locality, resembling them in other respects, in having a smaller umbilicus, more , 

 rapidly enlarging whorls, and a more elevated spire. 

 Locality and position: Same as preceding. 



STRAPAROLLWS SIMILIS, Vlir. PLANUS. 



PI. 19, fig. 5 a, 5b, 5c. 



Straparollus similis, y ax. planus, Meek and Worthen, June, 1861. Proceed. Acad. 

 Nat. Sci., Philad., p. 146. 



This form differs from the last in having its spire completely flattened so as 

 to be upon a level with the last turn, and in having a slightly larger umbilicus; 

 while the angle on the under side of the body whorl is a little farther out from 

 the umbilical side. The flattened space ou the upper side of its whorls also 

 differs in sloping inwards instead of being horizontal, and its suture seems to 

 be more distinct. Notwithstanding these differences, these forms agree so very 

 nearly in size and other respects, that- we do not feel quite warranted in re- 

 garding them as distinct species. Should it be thought necessary, however, to 

 separate them specifically, the form under consideration can take as a specific 

 name that by which we have designated it as a variety. 



It is an interesting fact that these two forms present exact miniature repre- 

 sentations, of the two varieties of S. pentangidatus, Sowerby (sp.). The fact, 

 however, that the shells under consideration show all the appearances of mature 

 growth, and never attain more than one-twentieth the size of S. pentangulatus, 

 while they have only two or three whorls less, is, we think, sufficient reason 

 for regarding them as distinct. 



Locality and position: Same as preceding. 



CEPHALOPODA. 



Genus OKTHOCEKAS, Auct. 

 Orthoceras expansum, M. and W. 



Orthoceras expansion, Meek and Worthen, Oct., 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 468. 



Shell having the form of a moderately compressed, rapidly 

 tapering cone;, section subcircular, near the smaller end, but 



