PROOFS, ILLUSTRATIONS, AUTHORITIES, ETC. xxiii 



rocks of Scotland, the exo-skeleton presents the form of large plates, 

 either symmetrical, or articulated symmetrically by straight 

 sutures, like the shell of the lobster. The large calcified dermal 

 shield which protected the head of the Cephalaspis, has often been 

 mistaken for that of a trilobite of the division Asaphus. These, of 

 course, are but analogies ; and the invertebrate-like condition of the 

 skeletons of the known palaeozoic fishes was doubtless associated 

 with a general plan of organization essentially vertebrate and 

 piscine. But we can never hope to arrive at the truth, as it re- 

 spects the course of creation on this planet, if we voluntarily shut 

 our eyes to the fact and the bearing of these analogies. 



" The contrasted states of the exo and endo- 



skeletons described by the Huuterian Professor in the Microdon 

 radiatus of the secondary epoch, may have been associated with as 

 advanced a development of the soft parts, as we find in the few 

 ganoidal fishes that exist at the present day ; but, the lower embryotic 

 condition of the vertebrate skeleton being demonstrated, not only 

 in that but in many other contemporary ganoids, it cannot be ad- 

 mitted that * the fish of the secondary rocks are as fully developed in 

 their organization as those now living.' 



"To the arguments against that succession on which Sir Charles 

 Lyell founds his statements, that no ichthyic type is more elevated 

 than the cartilaginous fishes of the Upper Silurian group, and that 

 the fish of the secondary rocks are as elevated as any now living, we 

 will finally reply by recalling the remarks which the study of those 

 ancient fossil fishes has elicited from the great founder of fossil 

 ichthyology. Besides the incomplete development of the back-bone, 

 M. Agassiz points out other striking traits of an embryonic cha- 

 racter. The cephalaspids of the old red sandstone were shaped like 

 the tadpoles of Batrachia ; the breathing organs and chief parts of 

 the alimentary apparatus were aggregated with the proper viscera of 

 the cranial cavity in an enormous cephalic enlargement; the rest of 

 the trunk was for locomotion, and dsvindled to a point. The posi- 

 tion of the anal fin proves the vent to have been situated, as in 

 tadpoles, immediately behind the cephalic-abdominal expansion. In 

 the Pterichthys, the mouth was small and inferior, as in the 

 young tadpole; and there are long fin-like appendages, projecting 

 from the sides of the cephalic enlargement, like the external 

 gills of the Batrachian and Selachian larvae." Quarterly Review, 

 Sept. 1851. 



" It was not till the time of the chalk formation that the two other 

 orders, the Ctenoid and the Cycloid, which almost exclusively pre- 

 vail in the present creation, made their appearance. The first types 

 of these orders belong for the most part to extinct genera allied to 

 our Clupeae and Tunnies. In this epoch fresh-water fish were still 

 wanting. The fishes of the tertiary epoch are much more nearly 

 related to those of our own times ; a great number belong to genera 

 now existing : we find true Tunnies, true Clupese, true Anchovies, 

 true Smelts, and fresh-water fishes well characterised, such as Pikes, 



