beede: upper permian red beds. 155 



*'In first describing this species, we called attention to its 

 close relations to E. speluncaria Schlot. (sp.), and stated that 

 we were aware it would not be easy always to find character- 

 istic differences by which certain varieties of these two forms 

 could be distingushed. Every naturalist, however, must have 

 met with analogous cases, where the varieties of two closely 

 allied but variable species approximate, and, as it were, min- 

 gle together, so as to render it sometimes extremely difficult 

 to separate them ; while the normal forms of each are so 

 clearly distinct as to leave no doubt on the mind that they 

 belong to different species. This, we think, is the relation 

 the Kansas shells bear to E. spelwicaria, although we are 

 aware some of our friends entertain the opinion that they are 

 not distinct. 



"It is true some specimens agree almost exactly with such 

 varieties of E. speluncaria as are represented by figures 15, 17, 

 20, and 21, plate XIII, of King's work on the Permian fossils 

 of England ; yet, out of hundreds of individuals collected and 

 seen by us in Kansas, we have never met with one present- 

 ing the peculiar lobed and sulcated posterior so characteristic 

 of the well-developed normal forms of E. speluncaria, such, 

 for instance, as figures 5, 6, 7, 8, 9, 10 and 11 of plate XIII 

 of King's work cited above. Again, none of our Kansas 

 specimens, with a solitary exception^ has had the beak of the 

 right valve so gibbous, or near so elevated, as those repre- 

 sented by the figures last above cited ; and in this single ex- 

 ception the shell differs so widely in other respects that, if not 

 a monstrosity, we can but regard it as belonging to a distinct 

 species from that under consideration, as well as from E. 

 speluncaria.' 



While differences of opinion as to the limits of definition 

 of the species of the genus exist, most all will agree that it 

 is an unusually variable one. I have quoted Waagen on this 

 point already,'- and agree very well with his conclusions. 



In the Pennsylvanian and Permian of Kansas there are many 

 of these fossils which possess the lobation of the shell to a 

 varying degree. While I have studied many from the oolite 

 -of Kansas City and the Kickapoo limestone at Lawrence, and 



52. Kan. Univ. Quart., Ill, p. 79, 1899. From Pal. Ind. Prod. Limestone Foss., Ill, p. 27*5. 



