PLATE XXV. 
PAGE 
Lettering: E. G., External gingival canal; I. G., Internal gingival canal; 
G.G., Gingival groove; D. C, Dental canal. 
Fig. 1. Cetotherium parvum Trouessart 44 
1. Section of left mandibular ramus. After Cope, Proc. Amer. 
Philos. Soc, Vol. XXXIV, PI. VI, Fig. 6. X Vs 
Fig. 2. Tretulias buccatus Cope 52 
2. Section of left mandibular ramus. After Cope, Proc. Amer. Philos. 
Soc, Vol. XXXIV, PI. VI, Fig. 2. X Va 
Fig. 3. SI^H0^'0CETUS expansxis Cope 45 
3. Section of left mandibular ramus. After Cope, Proc. Amer. Philos. 
Soc, Vol. XXXIV, PI. VI, Fig. 5. X Vs 
Fig. 4. SlPHONOCETU.9 CLARKEANUS Cope 47 
4. Section of left mandibular ramus. After Cope, Proc. Amer. Philos. 
Soc, Vol. XXXIV, PI. VI, Fig. 4. X 1/3 
Fig. 5. SiPHONOCETus PRiscus Leidy 46 
5. Section of left mandibular ramus. After Cope, Proc. Amer. Philos. 
Soc, Vol. XXXIV, PI. VI, Fig. 3. X % 
Fig. 6. Ulias 3I0RATUS Cope 50 
6. Section of left mandibular ramus. After Cope, Proc. Amer. Philos. 
Soc, Vol. XXXIV, PI. VI, Fig. 1. X 1/3 
Fig. 7. Cetotherium polyporum Cope 47 
7. Section of left mandibular ramus. After Cope, Proc. Amer. Philos. 
Soc, Vol. XXXIV, PI. VI, Fig. 7. X 1/3 
Fig. 8. Cetotherium cephalum Cope 44 
8. Section of mandibular ramus from Maryland, distal of the middle. 
After Cope, Proc Amer. Philos. Soc, Vol. XXXV, PI. XII, Fig. 
3. X 1/3 
Fig. 9. Rhegnopsis palaeatlanticus Leidy 45, 46 
9. Section of mandibular ramus from Virginia. After Cope, Proc. 
Amer. Philos. Soc, Vol. XXXV, PI. XII, Fig. 5. X Vs 
Fig. 10. Cetotherium leptocentrum Cope 47 
10. Section of mandibular ramus from Virginia. After Cope, Proc. 
Amer. Philos. Soc, Vol. XXXV, PI. XII, Fig. 1. X % 
Fig. 11. Cetotherium davidsonii Cope 34 
11. Section of mandibular ramus from California. After Cope, Proc. 
Amer. Philos. Soc, Vol. XXXV, PI. XII, Fig. 4. X 1/3 
Fig. 12. Mesocetus siphunculus Cope 34 
12. Section of mandibular ramus from Virginia. After Cope, Proc. 
Amer. Philos. Soc, Vol. XXXV, PI. XII, Fig. b. 
Fig. 13. Cetothekium cephalum Cope 44 
13. Section of mandibular ramus represented in Fig. 8, proximal of 
the middle. After Cope, Proc Amer. Philos. Soc, Vol. XXXV, 
PI. XII, Fig. 2. X 1/3 
17 
