64 OLD RED SANDSTONE FISHES. 



synonymy. Different parts of the same species have been described as different 

 genera, while in other cases remains of fishes having no affinity with them have 

 been mixed up and confounded with those of true Asterolepidse. 



As regards the affinities of the group, which have furnished much food for 

 theory, it will, I think, be wiser to postpone the consideration of this interesting 

 subject until the descriptive part of the work has been accomplished. I propose, 

 therefore, in the first place, to go through the British members of the family, genus 

 by genus and species by species, and then in a concluding chapter to discuss the 

 limits of the family, and to enter into the probable relationship of the Asterolepidse 

 to other fossil forms, and to fishes in general. Meanwhile the well-known facts, 

 that their dermal plates are composed of true bone, that they had a well-developed 

 lateral sense-canal system on the body and head, and that Pterichthys at least pos- 

 sessed a tail covered with scales, and provided with a dorsal fin, and a genuinely 

 piscine heterocercal caudal, furnish pretty conclusive evidence that the Astero- 

 lepidae were actual fishes, and that they were not specially related either to Asci- 

 dians, Crustaceans, or Arachnids. 



In pursuing my studies on these and other fishes of the Devonian epoch I have 

 of course largely drawn my material from the rich collections in the Edinburgh 

 Museum of Science and Art ; but I have also availed myself of the privilege of 

 examining the magnificent series in the British Museum, presided over by Dr. 

 Woodward, F.R.S., Keeper, and Mr. A. Smith Woodward, F.L.S., Assistant 

 Keeper of the Geological Department, to whom for their kindness and courtesy my 

 best thanks are due. Of exceeding value is also the collection of Old Red 

 Sandstone fishes in the Museum of Practical Geology, Jermyn Street, London, in 

 consulting which I have always met with the most friendly reception from Sir A. 

 Geikie, F.R.S., and Mr. E. T. Newton, F.R.S. My thanks are also due to Pro- 

 fessor McKenny Hughes, F.R.S., of Cambridge, Professor Green, F.R.S. , of 

 Oxford, Professor Boyd Dawkins, F.R.S., and Mr. W. E. Hoyle, of Manchester, as 

 well as to the authorities of the museums at Elgin and at Forres, for the ready 

 access which they have always afforded me to the collections under their charge. 

 To other sources of material and of information, and to other friends who have 

 generously assisted me, I shall have frequent occasion in the course of the following 

 descriptions to make my grateful acknowledgments. — R. H. T. 



Terminology of the Asterolepid^e. 



Before entering into the description of individual forms, it is first of all necessary 

 to understand the general structure of an Asterolepid, and to know the names by 

 which the various parts found in a fossil state may be distinguished. For this 



