Title: Ivory Identification Guide - U.S. Fish and Wildlife Service Forensics Laboratory
Headings: 

Content: The cementum frequently displays longitudinal cracks which follow the depressed areas of the spiral pattern. As a result, narwhal tusk cross-sections are rounded with peripheral indentations. The cementum is separated from the dentine by a clearly defined transition ring. Like killer and sperm whale teeth, the dentine can display prominent concentric rings. The pulp cavity extends throughout most of the length of the tusk giving cross-sections a hollow interior. Click to see cross section of narwhal tusk
HIPPOPOTAMUS
(Hippopotamus amphibius)
Upper and lower canine and incisors are the most common sources for hippo ivory. Each type of tooth has distinctive gross morphology. Close examination of a cross-section of hippo dentine with the aid of a 10X hand lens reveals a tightly packed series of fine concentric lines. These lines can be regularly or irregularly spaced. The orientation of the lines will follow the overall shape of the particular tooth.