6o Bulletin American Museum of Natural History. [Vol. XIX, 



Pachyrhizodus caninus Cope. 

 Plate III, Figs, i and 2. 



Pachyrhizodus caninus Cope (E. D.), Proc. Amer. Philos. Soc, XII, 

 1872, p. 344; Rept. U. S. Geol. Surv. Mont. etc. 1872, p. 348; 

 Bull. U. S. Geol. and Geog. Surv. I, No. 2, 1874, p. 42; Vert. 

 Cret. Form. West, 1875, pp. 221, 276, pi. 1, figs. 1-4. — Crook 

 (A. J.), Palceontogr. XXXIX, 1892, p. 109. — Loomis (F. B.), 

 Palseontogr. XLVI, 1900, p. 262, pi. xxvii, figs. 10-12. — Stewart 

 (A.), Univ. Geol. Surv. Kansas, VI, 1900, p. 355, pi. lxx,^figs. 2-6. — 

 Woodward (A. S.), Cat. Foss. Fishes, IV, 1901, p. 44. — Hay 

 (O. P.), Bibliog. and Cat. Foss. Vert. N. A. 1902, p. 387. 



Pachyrhizodus latimentum Cope (E. D.), Proc. Amer. Philos. Soc. XII, 

 1872, p. 346; Rept. U. S. Geol. Surv. Mont. etc. 1872, p. 348; 

 Bull. U. S. Geol. and Geog. Surv. I, No. 2, 1874, p. 42; Vert. 

 Cret. Form. West, 1S75, pp. 223, 276, pi. 1, fig. 5; pi. li, figs. 1-7. 

 — Loomis (F. B.), Palseontogr. , XLVI, 1900, p. 263, pi. xxvi, 

 figs. 7, 8. — Stewart (A.), Univ. Geol. Surv. Kansas, VI, 1900, 

 p. 357, pi. Ixviii; pi. Ixx, figs. 9, 10. — Woodward (A. S.), Cat. 

 Foss. Fishes, IV, 1901, p. 42. — Hay (O. P.), Bibliog. and Cat. 

 Foss. Vert. N. A. 1902, p. 388. 



Pachyrhizodus curvatus Loomis (F. B.), Palaeontogr. XLVI, 1900, p. 

 265, pi. XXV, figs. 6-8. — Woodward (A. S.), Cat. Foss. Fishes, 

 IV, i9oi,p. 44. — Hay (O. P.) , Bibliog. and Cat. Foss. Vert. N. A. 

 igo2, p. 388. 



The writer has ventured to unite the two species which 

 Prof. Cope has described under the names Pachyrhizodus 

 caninus and P. latimentum. The types of these are in this 

 Museum, that of P. caninus having the number 1881; that 

 of P. latimentum the number 1758. Besides these, there are 

 various jaws and other parts which were collected for Prof. 

 Cope by Messrs. Sternberg and Hill during the year 1877. 

 In attempting to apply to this material the characters as- 

 signed by Cope to his two species the writer has become con- 

 vinced that the differences are due partly to individual 

 variations and partly to distortions during fossilization. The 

 various collections indicate that the bones of this species were 

 soft and spongy, so that they easily suffered compression and 

 distortion. Jaw bones of the opposite sides of the same in- 

 dividual are sometimes so different that one is convinced 

 with difficulty of their identity. The groove which divides 



