448 The Ohio Naturalist. [Vol. XII, No. 3, 



above strata in which Platystrophia ponderosa is rare. It is im- 

 portant to remember that the globular bryozoan frequently referred 

 to Prasopora in this discussion has not been subjected to micro- 

 scopic investigation, so that its real affinities remain to be deter- 

 mined. 



Northwest of Ellisburg, Prasopora occurs eleven feet below a 

 light blue clay layer containing clay nodules. In the lower part 

 of the intervening section, interpreted as upper Arnheim, Platys- 

 trophia ponderosa occurs. Prasopora is abundant on the hill 

 supporting the stand-pipe northwest of McKinney, in Lincoln 

 county; also along the railroad, a short distance south of Moreland. 

 About a mile south of Shelby City, where the pike crosses Knob 

 Lick branch, Prasopora occurs below strata containing Platys- 

 trophia ponderosa. The locality at the former site of the creamery, 

 three and a half miles southwest of Stanford has been mentioned. 

 All of these localities belong to the territory in which Leptaena 

 richmondensis and Rhynchotrema dentata are absent. Even 

 Prasopora is not present at all of the exposures regarded as belong- 

 ing to the Arnheim horizon, at least approximately. In its 

 absence, the identification of the Arnheim becomes difficult, in 

 the territory under discussion. 



Possibly the difficulty of identifying the Arnheim in some 

 parts of Casey and Lincoln counties may be due to a thinning out 

 of this member of the Richmond southeastward. This might 

 account also for the disappearance of the Leptaena and Rhyncho- 

 trema fauna at all the more southern exposures in Kentucky, 

 with the single exception of the exposure along Damron creek, in 

 the northeastern corner of Adair county. 



13. Diastrophic movements during deposition of the Arnheim. 



The Arnheim period of deposition apparently began with a 

 slight diastrophic elevation on the southeastern side of the Arnheim 

 sea. This gave rise to the thin bedded, unfossiliferous, argilla- 

 ceous strata forming a characteristic part of the Lower or Sunset 

 division of the Arnheim, in Kentucky, from Lincoln county north- 

 ward beyond the mouth of the Red river. It produced apparenth* 

 the paucity of life in the argillaceous limestones forming the 

 Lower Arnheim farther northward, from the vicinity of Howards 

 Mill to the Ohio river at Maysville. Still farther northward, 

 there was a sudden extinction of the great Platystrophia pon- 

 derosa colonies which characterized the Mount Auburn in many 

 parts of Ohio. In Indiana, there is no evidence of any consider- 

 able change either in the character of the sedimentation or of the 

 enclosed fauna on passing from the Mount Auburn to the Lower 

 Arnheim. 



Possibly the lower Arnheim thins out southward also on the 

 western side of the Cincinnati geanticline, at least locally. The 



