45° The Ohio Naturalist. [Vol. XII, No. 3, 



The species of Dalmanella, which occurs so abundantly in the 

 Arnheim of southwestern Ohio, is found also in the adjacent parts 

 of Indiana. vSouthward, it is absent until the exposures at Newsom 

 and Clifton, in western Tennessee are reached. There may have 

 been a connection between southwestern Ohio and Tennessee by 

 a path farther west than any now exposed. The origin of the 

 Dalmanella found in the Arnheim of southwestern Ohio and the 

 adjacent part of Indiana, however, may have been indigenous. 

 In Franklin and Dearborn counties, in Indiana, Dalmanella 

 occurs at various levels in the Arnheim, being quite abundant in the 

 low^er half. It occurs in the same area also at various levels in 

 what is identified as the Mount Auburn. Near Brookville, it is 

 very abundant in the Corryville, and it occurs in moderate numbers 

 also in the more northern exposures of the Corryville in Ohio. 

 Not all of the specimens of Dalmanella found in the Fainiiount 

 belong to Dalmanella fairmountensis. That species has a rather 

 restricted geographical range. A derivative of Dalmanella 

 multisecta is rather widely distributed at the Strephomena plano- 

 convexa horizon, and it is from the Eden Dalmanella multisecta that 

 the Arnheim species may have evolved. The vertical distribution 

 of Dalmanella is limited to the lower part of the upper or Oregonia 

 division of the Arnheim southeast of Butler and Hamilton counties, 

 in Ohio, suggesting an entry into this area from the northwest, 

 from Indiana. 



Leptaena richmondensis is one of the most widely distributed 

 species found in the Arnheim. It occurs almost over the entire 

 area investigated, both north and south, wherever the Arnheim 

 is known. It is a typical eastern Richmond species, and was 

 certainly not derived from Leptaena unicosta, the western Rich- 

 mond form. It is the latter species which has varied most from 

 the primitive form. Leptaena richmondensis is least abundant in 

 sotitheastern Indiana, and is entirely absent in southern Kentucky, 

 along the Cumberland river. It is most abundant in southwestern 

 Ohio and in central Kentucky. Probably the latter areas were 

 once connected by Arnheim deposits which since have been 

 eroded away, since there is a small area in western Lincoln and 

 eastern Casey and Boyle counties, in Kentucky, from which 

 Leptaena is ab.sent. Rhynchotrema dentata is absent from the same 

 area, in central Kentucky, and may have used the same hypo- 

 thetical passage a moderate distance northward. 



Rhynchotrema dentata is much more abundant southwards, in 

 Kcntuck}', than northwards, and in Ohio and Indiana it is confined 

 to the most southern exposures. Certainly, it would be difficult 

 to imagine a northern origin for this species, as far as its entry 

 into the Arnheim is concerned. Moreover, it occurs also at 

 Goodletsville, Newsom, and Clifton, in western Tennessee. As 

 in the case of Dinorthis carleyi, and Leptaena richmondensis, it had 



