54 MONOGRAPH OP DURA DEN. 



plate, siaiilar in form, in position and structure, to that found in Pterkhthys. 

 This plate characterizes the ventral region of the fish, and thus afft)rds re- 

 markable testimony to the accuracy of the view I have taken in assigning 

 the like position to the homologous plate in Pterichthysy* 



Since the publication of this paper I believe M. Agassiz has not again 

 turned his attention to the subject, nor amidst his numerous elaborate inves- 

 tigations has had either leisure or opportunity of doing so. But in a commu- 

 nication I recently had the honour to be favoured with, he says, " You must 

 know that I have had no opportunity of making a renewed examination of 

 the Dura Den fossils since I was favoured with a sight of those you forwarded 

 to me at Neufchatel twenty years ago, and tliat I have no chance whatsoever 

 of making now the comparisons necessary to verify the suggestions of Sir 

 Philip Egerton. At the same time, I have, like all those who know him, 

 such implicit confidence in his accuracy and ability to decide in such matters, 

 that I should feel reluctant to insist upon the correctness of my own opinions, 

 expressed so long ago, in contradiction to|his views, resulting from a more 

 recent examination of the facts. I have not the remotest doubt that Sir P. 

 Egerton has shown a closer affinity to exist between the Pamphractus Ander- 

 soni and the species of Pterichthys proper, than I supposed there was between 

 them. Still I am not yet, on that account, satisfied that the genus pamphrac- 

 tus must be given up. Judging from my figures and descriptions, I am now 

 inclined to believe that coccosteus and cephalaspis can no longer remain in 

 one and the same family with pterichthys. Again, the views I have pre- 

 sented respecting the limitation of genera in my Essay on Classification, will 

 require a revision of all the pterichthys, with reference to their genuine char- 

 acters, and I look forward, from the indications I can gather in my own 

 work, to the necessity rather of subdividing the species which have been 

 united as pterichthys into several genera, than to the propriety of combining 

 pamphractus and pterichthys. I throw out this suggestion for your considera- 

 tion, and must leave it to the palaeontologists who have the necessary materials 

 on hand finally to settle these points."f 



While these generic resemblances, as well as distinctions, must be left for 

 future revision and determination, let it be observed that pterichthys, cepha- 

 laspis, coccosteus, and pamphractus are all of the family type of Lepidoides, 

 and have such affinity in outward form as readily, in mutilated specimens at 

 least, to be mistaken for each other. The appendages of the head, having 

 the appearance of wings, suggested the terms of Pterichthys, or the winged 

 fish {pAeros, a wing ; ichthys, a fish). The plates covering the body, according 

 to their number and position and form, gave rise to the generic distinctions, 

 and the species of each have been determined by minor differences. The 

 external organs in all are enamelled, and discover, like all the Crustacea of 

 the period, the tubcrculated surface. The pterichthys of the northern coun- 

 ties, in Cromarty, Moray, and Elgin, vary in size from nearly a foot to an 

 inch in length, and the wings generally are extended perpendicularly to the 

 body. The pamphractus of Dura Den are all of a size, from two inches to 



* Vol. iv. p. 308. t I>'itecl Boston, Cambridge, U.S.. ilh December 1858. 



