The Faniia of the i\la.vz'illc Limestone. 379 



The plications and intervening spaces, when the surface is well 

 preserved, are marked b}' fine longitudinal lines, showing even 

 on partially exfoliated specimens, and are also crossed by still 

 finer transverse stria? which imdulate in crossing the plications, 

 and on perfectly preserved surfaces appear to be minutely setose 

 on their edges. 



"The species is extremely variable in its general outline, as 

 exhibited among the collections from all of the many localities 

 from which I have examined specimens, especially in the ex- 

 tension of the hinge-line, and the proportional width of the shell 

 below, and also in the prominence of the mesial fold ; but the 

 form of the plications and the character of those marking the 

 fold and sinus are usually the same in all ; while the most con- 

 stant and persistent character, and one 1 have been able to 



Fig. 11. — Spirifer kcokuk. Pedicle vah'e. (After Whitfield.) The form 

 of this species varies greatly in the Maxville limestone. 



detect on specimens from almost every locality noticed, consists 

 of the minute structiu'e of the surface. I have lately examined 

 a large number of examples from the limestones and sandstones 

 of the Coal Measures of New IMexico, which correspond ex- 

 actly with those figtu'ed by Prof. Marcou imder the name 5*. 

 Rock\inontana, and find them showing all the variations in form 

 noticed among the Keokuk, St. Louis, Chester and Coal Measure 

 limestones of Ohio and the West, and am thoroughly convinced 

 they cannot be separated, even as local varieties, with any degree 

 of safety or satisfaction [Whitfield, 1895]."' 



In the above bibliography Weller's arrangement has been 

 followed, except for the listing of Herrick's S. increhesceiis, 

 which is undoubtedly the same as the other Maxville Spirifers. 

 Had the writer been bolder and followed his own inclinations. 



