TUB NAUTILUS. 



135 



Pearl River. Sabine River. 



1. Anodontoides, Anodontoides, 



2. Gracilis, Gracilis, 



3. Cornutus, Cornutus, 



4. Aspera, Aspera, 



5. Perplicata, Perplicata. 



6. Trapezoides, Trapezoides, 



7. Heros, Heros, 



8. Purpurata, Purpuraia, 



9. Conlragosa, Confragosa, 



10. Donaciformis, Donacifornus, 



11. Elegans, Ele^uns, 



12. Tuberculata, Tuberculata, 



13. Castaneus, Castaneus, 



14. Riddelii, Riddelii, 



15. Cerinus, Cerinus, 



16. Concestator, Nigerrimus, 



17. Inflata, Arapliiclia;na, 



18. Excavata, Satur, 



19. Claibornensis, Hydiana, 



20. Beadleana, Askewii, 



21. Refulgens, ) (Nodifera, 



22. Sphaerica, ) "(Mortonii, 



23. Ebenus, 



24. Crassidens, 



25. Coraplanata. 



Notwithstanding the absolute identity of the first fifteen species, 

 yet there is a well-marked tribal difference between the two sets, 

 the Pearl river U. heros being nearly full-blooded boykiniana^ and 

 with a yellow nacre. 



The U. riddelii of Pearl river inclines towards rubidus, some being 

 of a warm, rich rose color. These Pearl river shells vary also in 

 having the successive lines of growth so heavily impresseil that the 

 shell sometimes has humps as well defined as in the well-known U. 

 dromas Lea. 



Perhaps the most interesting feature, however, lies in the list 

 where the species differ : 



U. concestator vs. nigerrimus. Large suites of both show their 

 identity, with only slight differences. U. nigerrimus is only a variety 

 of concestator. 



