The Fauna of tJic Maxinllc Limestone. 381 



the pHcatic^ns, in their grcnvth toward the anterior end, bend 

 deciderlly toward the lateral margins. However, the mesial fold 

 is sometimes much more abrupt with a suppression of all of its 

 I'tlications except two and in this res])ect the specimens resemble 

 S. keokiik. In the up]:;er half another small form is found which 

 resembles .S\ keokiik somewhat more closel}' than it does S. 

 roelcynioiitaiiiis. In this same division and especially in the Olive 

 Furnace Shaft occui- still other forms which are larger and 

 coarser and which can with eciual ])r()priety be referred to 

 cither .S\ keokitk or S. increbeseens. 



In the ]\laxville limestone, therefore, the separation of .9. 

 keolciik and A", inerebeseeiis is attended with, a great deal of 

 difficulty if not im])racticable. The same trouble is experienced 

 in the attempt to refer some sj^ecimens to S. rockxniontainis 

 ( 1858) on the one hand and to .S\ keokiik { 1858) on the other. 

 That this should be the case is not at all surprising when the 

 principles of evolution are taken into consideration ; and when 

 this is done one species will probably be the result. 



llori.voii and localifv. — Maxville limestone. 

 Upper zone : Mouth of Buckeye Fork, Fultonham ; Gladstone 



Mills, Thompson Residence, White Cottage. 

 Lower zone: Cut No. 4, Mt. Perry-b'ultonham. 

 Undetermined zone: TTar])er Shaft, Olive b^umace. 



DI^LASMA TURGIDA-Hall. 



IS.Vi. Terebratula turgida. Hall, Trans. Albany Tnst., Vol. IV, p. 6. 



St. Loui.s limestone: Alton, Illinois; bloominoton and Spergen 

 Hill, Indiana. 

 18S-J. Terebratula turyida. W'hitlicdd, I'.ull. .\m. Mus. Nat. Hist., Vol. 

 I, p. 54, pi. (;, figs. 5;S-58. 

 St. T-ouis group: Indiana, Towa, Illinois and Missouri. 

 IHS:?. Tcrehratnhi turijida. Hall, Ind. l)ei)t. Ccol. \;it. Hist., li'th Rept., 



p. ;:;!(;, i)l. l'd, figs. ^^^-^^s. 



St. Louis group: .Mton, Illinois: IJloomington, Lanesvillc and 

 Spergen Hill, Indiaiia. 

 1891. Terebratula turgida. Whitfield, Ann. X. ^'. .\cad. Sci., Vol. V, 



]). :.8(i, pi. v^. figs, ^l, 2-_'. 



MaxvilK' limestone: Maxville and Xewtonville, Ohio. 



