No. 379. ] DEVONIAN PTYCTODONTIDA. 475 
of the Russian forms described by Pander, but lacking the 
symphysis and having the tritoral area imperfect, was made by 
Rohon the type of a second European species, P. major. 
Apparently the left lower jaw is portrayed in the illustrations, 
although as far as one may judge from Pl. I, Fig. 2, of Rohon’s 
.paper the direction of the tritoral punctz is forward and out- 
ward instead of forward and inward. This character, however, 
as will presently be shown, is not an infallible clue to the 
orientation. The same author also mentions the occurrence 
of certain dorsal fin-spines having a tuberculated ornament, 
which he thinks may possibly have pertained to this genus. 
(3) P. molaris (Figs. 28-30).— Yet another European 
species is that recently figured by the writer under the name 
of P. molaris,2 from the Devonian of Prüm, in the Eifel Dis- 
trict of Rhenish Prussia. The type specimen (Fig. 28) is a 
very perfect dental plate contained in the Schultze Collection, 
now the property of the Museum of Comparative Zoology. It 
represents the left lower jaw and is 6 cm. in length, but at 
least I cm. has been broken away from the posterior end. Its 
maximum thickness, which occurs just below and behind the 
tritor, is 1.2 cm. The tritoral puncte are directed forward and 
outward, as in P. major. The forward portion of the tritoral 
area has been injured by abrasion, and so, too, has the cutting 
edge, which extended from the anterior end of the tritor as far 
as the symphysial beak, a distance of rather less than 2 cm. 
The tritor itself in this specimen is 2.4 cm. long, and its maxi- 
mum width .7 cm. The outer face of the jaw is comparatively 
Straight, the inner slightly bowed inward posteriorly. Fine 
concentric markings having a more or less longitudinal direc- 
tion, such as occur in all well-preserved Ptyctodus jaws, can 
with difficulty be made out on both faces, owing to an adventi- 
tious glaze which covers the fossil. 
This specimen has the anterior portion exceptionally well 
preserved. The front margin is slightly rounded, extends 
upward to form a strong prehensile beak, and also projects 
1 Rohon, J. V. Beitrag zur Kenntnis der Gattung Ptyctodus, Verhandl. 
mineral. Gesellsch. St. Petersburg [2], vol. xxxiii (1895), pp. 1-16. 
2 Ann. Rep. Iowa Geological Survey, vol. vii (1897), p- 115, Fig. 10 B. 
