54 EXPLANATIONS. 



character were writing, publicly and privately, of 

 the cephalaspis and coccosteus, as apparently links 

 between the Crustacea and fish, the vertical mouth 

 of the latter animal being particularly cited, as a 

 feature indicating the intermediate character. In 

 what the reviewer calls " the excellent work of our 

 meritorious self-taught countryman," Mr. Hugh 

 Miller, published in 1841, the apparently crusta- 

 cean character of these fishes is repeatedly referred 

 to.* Not having access at the time to the work of 

 Agassiz, I deemed myself safe in tiTisting to the 

 report of this industrious inquirer and ingenious 

 writer, whose volume was then newly published. 



The above argument relates to the general fact 

 of the first fishes being placoidean. It is neces- 

 sary, also, to meet the inquiry why there should 



* Mr. Miller calls upon his readers to " mark the form of the 

 cephalaspis, or buckler-head, a fish of the formation over that in 

 which the remains of the trilobite most abound. He will find," 

 he says, " the fish and crustacean are wonderfully alike : the 

 fish is more elongated, but both possess the crescent-shaped head, 

 and both the angular and apparently jointed body. They illus- 

 trate admirably how two distinct orders may meet. They exhibit 

 the joints, if I may so speak, at which the plated fish is linked to 

 the shelled crustacean. Now, the coccosteus is a stage further on ; 

 it is more unequivocally a fish ; it is a cephalaspis, with a Fcale- 

 covered tail attached to the angular body, and the horns of the 

 crescent-shaped head cut off." — Old Red Sandstone, p. 54. 



