76 bulletin: museum of compakative zoology. 



noticed that in one species, E. giganteus, the cross-section is slightly 

 asymmetrical. Whether this is due to accidental deformation, or is in- 

 dicative of a paired series referable to the upper jaw, there are at present 

 no means of determining, Campodus is the only genus in which the 

 teeth exhibit marks of contact with opposing series. 



Information i-egardhjg the mode of growth in Edestus is afforded by 

 the detached segments of E. heinrichi and E. minor '^ which are known, 

 Successional teeth are formed in the same way as in Campyloprion and 

 llelicoprion, the only difference being that the bases of the newer formed 

 segments ensheathe the older to a much greater extent. The first- 

 formed or " terminal segment " of E. heinrichi is not a " solid bone," as 

 stated by IS^ewberry,^ but possesses a gouge-like base the same as the 



Fig. 7. 



Edestus heinrichi N. & W. Coal Measures; Carlinville, Illinois. Series of seg- 

 ments belonging to a single individual. X 2- 



rest. In the specimen figured by him as a supposed terminal segment, 

 only the " denticle " [crown] is preserved, and the carbonaceous matrix 

 which originally filled the interior of the sheath might readily be mis- 

 taken at first sicrht for " bone " or vasodentine. In text-figure 7 are 

 shown several segments belonging to a single individual of E. heinrichi, 

 in which the mode of succession is clearly discernible. The original, 

 which forms part of the A, H. Worthen Collection in the Museum of 

 Comparative Zoology, is from the Coal Measures ("roof of no. 5 coal ") 

 at Carlinville, Illinois. The segments fit snugly into one another in 

 their natural position, but are shown slightly separated in the drawing. 

 Associated with this specimen either naturally or accidentally was a 

 fragmentary fin-spine of Ctenacanthus having a very coarse ornamenta- 



1 Ann. N. Y. Acad. Sci., Vol. IV., 1888, p. 120, Plate V., Figure 2a-Monogr. 

 U. S. Geol. Surv., Vol. XVL (1889), p. 223, Plate XXXIX., Figure 2a. 



