1897.] NEW YORK ACADEMY OF SCIENCES. 295 



The affinity of these teeth to Petalodus is also shown by one of 

 Mr. Davis' figfures of Petalodus acuminatus. As. in the work 

 cited above, PI. LIX., in which the root is divided like that of 

 Dacfylodus. We must look for the counterpart of McCoy's 

 Polyrhizodus magnus in such teeth as P. borosus, N. & W. 

 CReport of Geological Survey of Illinois; Vol. II., p. 49, PI. 3, 

 fig. 9), and in the multitude of broad, low, many rooted teeth 

 such as P. dentatus and P. ponticuhis, N., P. Littoni, P. arcuatus 

 and P. carhonarius, St. J. & W. There are certainly resemblances 

 among all these teeth, for they are members of one family, the 

 Petalodontidse, but the group to which we have given the name 

 Dactylodus and of which so many fine examples are now shown 

 well deserves to be distinguished by a special generic name. 



Dactylodus princeps, N. & W. 

 PI. XXIII., figs. 5, 5 a, 6 ( ? Ed.). 



In 1888 a figure and description of a very complete, but then 

 unique tooth was given in Vol. II. of the Report of the Geologi- 

 cal Survey of Illinois (p. 45, PI. 3, figs. 6, 6 a, 6 b) to which the 

 name Dactylodus princeps was given, and it was made the 

 tj'pe of the genus. Since then a large number of similar teeth 

 have come into my possession which enable me to give a some- 

 what more detailed description of the species than has been 

 hitherto possible. The specimen which was made the type is 

 a little larger than the average and yet it represents the species 

 well but some old and much worn teeth which I refer to it are 

 more massive. The variation in the man}' teeth which I have is 

 interesting, but they are alike in this that they are all unsymme- 

 trical, as is the type specimen, they have the anterior face 

 strongly arched in both directions and there is no ridge or 

 enamel fold at its base ; the upper margin is generally quite 

 obtuse and. except just along the abraided edge, the anterior face 

 is black. The posterior face is light gray, the enameled band 

 quite strong and usually gently arched, without a sinus. 



An unusuall}- symmetrical tooth from the St. Louis beds at 

 Greencastle, Indiana, exhibits an interesting feature in a broad 

 and deep cavity worn at the base of the posterior face of the 

 crown b}'^ the opposing tooth. This is a character that would 

 doubtless appear in the teeth of this species more frequently, 

 if the tenacious matrix were removed from their posterior faces. 



All my specimens are from the St. Louis limestone and most 

 of them were collected by Mr. William Mc Adams at Alton, 111. 

 (These specimens are now in the collection of Columbia Univer- 

 sity. Ed.). 



