DEVONIAN FISHES OF IOWA 217' 



that the teeth in question have been exposed to the action of 

 digestive fluids within the intestinal tract of other creatures 

 which swallowed them. Although the agency invoked is purely 

 conjectural, it accords well with the partial, very gradual, in 

 some cases uniform effacement of tubercles over the functional 

 surface of the tooth, when marks of wear are localized and very 

 distinct, and when the obliteration of tubercles is clearly of a 

 different order from mere mechanical abrasion. Moreover, 

 nothing is more likely than that the large numbers of Dipterine 

 fishes frequenting this particular locality, and whose remains, 

 together with those of Ptyctodonts, constitute a veritable 'fish- 

 bed,' afforded a tempting prey for whatever creatures of car- 

 niverous habit chanced to share the same environment. The 

 identity of the predatory foe we have imagined is of course a 

 matter of mere speculation, yet the inference is not improbable 

 that Ptyctodonts and Dipterines, in this locality at least, were 

 natural enemies. At all events the commingling of their remains 

 in such astonishing abundance over a limited area might be held 

 to signify something more than a fortuitous coincidence. 



It may be objected that Ptyctodonts and Dipterines were not 

 mutually predatory, nor did one group subsist upon the other, 

 because both have a similar type of dentition, adapted for the 

 comminution of hard-shelled prey, such as mollusks, brachi- 

 opods, echinoderms and the like ( " conchif rage " Dollo). In 

 view of the known habits of Lung-fishes, the objection probably 

 holds in so far as it may be questioned whether Dipterines 

 actually preyed upon Ptyctodonts ; but in the inverse sense the 

 objection does not hold if we may depend upon analogy with 

 the habits of modern Chimaeroids, which are singularly omniv- 

 orous, and able to injest objects of large size. Thus, in speak- 

 ing of the food-habits of the existing Chimaera colliei, Professor 

 Dean has the following note :,* 



"In C. colliei observations on about a score of individuals 

 showed a singular mixture of food. Most numerous were ver- 

 tebral columns of small isospondylous fishes, a few mollusk 

 shells, usually greatly crushed, a quantity of sand and fine 

 gravel, squid, nudibranchs and opisthobranchs, bits of cases, 



*Dean, B., Chimaeroid Fishes and their Development. Carnegie Inst. Wash 

 Pub. no. 3*. 1906, p. 20. 



