VERTEBRATES. 47 



The figures given of B. princeps represent (6) the anterior face; (6 a) the 

 posterior do; and 6 J, the profile section ; all natural size. 



Formation and locality : St. Louis limestone, St. Louis, Missouri. 



Dactylodus lobatus, N. and W. ^ c ^- / 



fw» f~ 



*r' 



PI. Ill, Fig. 1, 1 a. 



Teeth rather small, thin and flattened, crown elliptical, cut- i^l/fls *^ ' ^** 

 ting edge regularly arched, posterior face smooth, in weathered 

 specimens finely striated longitudinally, concave vertically, 

 nearly straight horizontally; anterior surface two-thirds as high 

 as posterior ; posterior coronal ridge formed by the imbricating 

 folds, bow-shaped, prominent, folds numerous, (5-6), sharp, fine 

 and parallel; root half the height and half the breadth of 

 crown, three lobed, lateral lobes acute, middle one larger and 

 emarginate. Height 9 lines; breadth 10 lines', height of crown, 

 including basal ridge, 6 lines; of root 3 lines. 



The single specimen of this species contained in the collection, seems to be 

 another connecting link between Petalodus of Owen, and Polyrhizodus of 

 McCoy. The crown is apparently precisely that of a Petalodus, and the root, 

 in its general form, is not unlike that of some Petalodi, except that it is deeply 

 lobed. A tooth, generically, and it is possible, specifically, identical with the 

 # one before us, has been described by Prof. Leidy under the name of Ctenopty- 

 chius digitatus. {Trans. Amer. Philos. Soc, Vol. XI, p. 90, PI. h,figs. 27, 28, 

 29). Judging from the figures and description only of that tooth, we should 

 say it was less symmetrical, the edge of the crown less thin and acute, the root 

 longer and broader than in our specimens. These differences may prove, how- 

 ever, to be dependent on the places which they occupied in the mouth. 



The peculiar and abnormal character of these teeth is strikingly illustrated 

 by the fact that an anatomist of so great learning, and so proverbially accurate, 

 as Dr. Leidy, should have reversed one of them, and have described as the 

 crown, what is shown by the three well marked and closely allied species before 

 us, to be the root. 



Figures 7 and 7 a, represent the posterior face and section, natural size. 



Formation and locality: St. Louis limestone, Alton, Illinois. 



