88 Upper Cretaceous Fauna from Tennessee [286 



Order Aspidobranchiata 



Eulimidae. Leiostraca 1 species 



Euomphalidae. Hippocampoides 1 species 



Turbinidae. Schizobasis 1 species 



Trochidae. Solariella 2 species 



Umboniidae. Teinostoma 1 species 



Delphinulidae. Urceoabrum 1 species 



Liotai 3 species. 15 



CLASS CEPHALOPODA 

 Order Nautiloidea 



Nautilidae. Eutrophoceras 1 species 



Order Ammonoidea 



Lytoceratidae. Baculites 3 species 



Turrilites 1 species 



Cosmoceratidae. Genus Scaphites 1 species 



Probably the most significant fact revealed by the above 

 list is that the number of univalve species is greater than the 

 number of bivalve species. However, all three orders of the 

 Pelecypoda are well represented. Of the Order Prionodes- 

 macea the three families represented by the greatest number 

 of forms are the Arcidae, Ostreidae and Mytilidae. The last 

 two had their beginning in the Paleozoic. The Arcidae ori- 

 ginated and suddenly became a prominent group in the latter 

 part of the Mesozoic and developed into very great import- 

 ance in the Tertiary. Each of these three families is repre- 

 sented by four genera at Coon Creek. Among the Anomalo- 

 desmacea there are three families and five genera. The 

 Teleodesmacea are well represented. Of this order probably 

 the individuals of the families Cardiidae, Veneridae, and 

 Corbulidae are most abundant. A comparison of the above 

 list with lists from the East Coast Cretaceous shows that the 

 bivalves are relatively less abundant in the Coon Creek hori- 

 zon than in corresponding horizons in New Jersey and the 

 Middle Atlantic States. Several genera such as Cuspidaria, 



15 Besides the above named genera there are probably thirteen 

 genera and more than that number of species whose generic relations 

 have not been determined on account of the fragmentary condition 

 of the material. 



