OrRTMANN: NAIADES OF THE GREEN RIVER DRAINAGE. 185 
Green River and Cumberland River, by way of the Ohio, was non- 
existent. 
In more recent times, when the present drainage features had been 
established, the situation became different, and an interchange of 
forms could take place; yet a number of them never took advantage 
of this opportunity. It seems that chiefly forms of smaller streams 
belong to this latter class, as is entirely natural. 
In order to bring out more clearly the fact, that there is a great 
contrast between the Cumberland and Green River faunas, it is well 
to give here a list of true Cumberlandian elements, present in the 
Cumberland drainage, and absent in Green River (see: Wilson and 
Clark, 1914; Ortmann, 1924 and 1925). 
1. Fusconaia barnesiana (Lea) *12. Micromya vanuxemensis (Lea) 
2. Quadrula intermedia (Conrad) 13. Dysnomia arcaeformis (Lea) 
*3. Pleurobema oviforme (Conrad) 14. Dysnomia brevidens (Lea) 
4. Pegias fabula (Lea) 15. Dysnomia lenior (Lea) 
5. Plychobranchus subtentum (Say) *16. Dysnomia haysiana (Lea) 
6. Dromus dromas (Lea) *17. Dysnomia lewisi (Walker) 
7. Actinonaias pectorosa (Conrad) 18. Dysnomia biemarginata (Lea) 
*8. Carunculina moesta (Lea) 19. Dysnomia turgidula (Lea) 
9. Medionidus conradicus (Lea) 20. Dysnomia florentina (Lea) 
10. Micromya trabalis (Conrad) 21. Dysnomia capsaeformis (Lea) 
11. Micromya taeniata (Conrad) 
The species marked with an asterisk (*) have representative forms 
in the Ohio drainage. The place of Pleurobema oviforme is taken by 
Pl. clava®; that of Carunculina mesta by C. glans; that of Micromya 
vanuxemensis by M. ortmanni; that of Dysnomia haysiana by D. 
sulcata (Lea); that of Dysnomia lewist by D. flexuosa. All these 
representatives have been found in Green River, with the exception 
of Dysnomia sulcata. An explanation of this condition requires 
special study, and may be similar to that indicated above in the case 
of Micromya vanuxemensis and ortmanni; yet these forms might in 
part indicate other possibilities in the development of these two 
faunas, since the distributional facts in these cases are not all of the 
same character. 
But there remain enough others, where the contrast is very striking, 
and this concerns chiefly nos. 4, 6, and 9, since here also the genera 
( Pegias, Dromus, Medionidus) are absolutely missing in the interior 
drainage. And with regard to No. 1 (Fusconaia barnesiana) and the 
® This case requires further study, see: Ortmann, 1925, p. 340. 
