I am having a tough time coming up with what these two teeth are. When I first pulled them out of the river I thought horse. Then looking closer I began to question that assumption because of the hollowness seen in both. Looking on line and through my Neophyte's Guide I then found a similar looking Sirenia molar. But then I also found a Neohipparium Eurystyle unerupted lower molar that looked like a possibility. Any help clarifying the ID on these would be appreciated.