42 Cephalaspides. 



majority of fishes having the embryonic forms of the fins and 

 of the head so strongly marked. 



These facts evidently afford us the key to the rank which 

 these families ought to occupy in an ichthyological system, and 

 a judicious application of embryology to the classification of 

 animals, cannot fail to be attended with the most beneficial 

 results, in bringing our zoological systems to perfection. If, 

 indeed, after having pointed out the anatomical affinities of 

 the fishes of the old red sandstone, we then . examine the 

 zoological relations in which they are found in regard to the 

 succeeding creations, we perceive, that of the five families 

 occurring in the old red sandstone, there is one, that of the 

 Cephalaspides, which is wholly confined to that formation ; 

 that there is another, the Sauroides, which is represented 

 only by a particular group, the Dipterians, likewise limited 

 to the old red ; that a third, that of the Acanthodians, is not 

 continued beyond the coal formation, and that only the 

 Celacanthes and the Cestraciontes reach more recent forma- 

 tions. 



Of all these families, it is likewise that of the Cephalaspides 

 which recedes most from the ordinary forms of other fishes, 

 to such a degree that one might easily, at the time of their 

 first discovery, misunderstand their nature, and take them for 

 animals belonging to other classes of the animal kingdom. It 

 is in this family that we have found the type of fishes with 

 winged appendages, represented by the genera Pterichthys, 

 Pamphractus, and Polyphractus, which, owing to the cuirass 

 of their bodies, formed of many pieces closely soldered, and 

 from their pectoral fins being transformed into recurved 

 stylets, have passed sometimes for tortoises, sometimes for 

 enormous aquatic Coleoptera. It is among the Cephalaspides 

 that we have found the curious genus Cephalaspis, whose 

 broad cephalar shield, with two eyes almost united in a 

 single orbit, had caused it be taken for a crustacean allied to 

 the Limulae or Trilobites, before becoming acquainted with 

 its scaly body and tail provided with vertical fins ; it is among 

 the Cephalaspides, finally, that we must place the Coccostei, 

 with their powerful cuirass and long flexible tail, which must 



