160 Miscellaneous. 



different from the few fishes yet found in the upper region only of 

 the Silurian system next below it. 



Mr. ^lurchison, during his extensive tour in Russia, in the late 

 summer, has enlarged our knowledge of the range of these cu- 

 rious fishes and of the old red sandstone over vast regions in the 

 nprth-east departments of Europe. Thus the ichthyological fauna 

 of the old red sandstone has within a few years been found to be 

 one of the richest and most prolific kind ; and its extinct species are 

 much more curious and remarkable than those of any other forma- 

 tion, by their deviation from the conditions of existing genera and 

 species. Their most characteristic feature is an immense develop- 

 ment of bony matter and enamel on the surface of the skin, thus 

 approaching to the external dermal skeleton of Crustacea and In- 

 sects. One of these fishes, the Pterichthys, is so largely and almost 

 entirely encased with bony plates and scales, that it was at first mis- 

 taken for a fossil Water-beetle. 



The nearest analogies we find among modern fishes to the great 

 development of bony matter and enamel upon the head and scales 

 of many of these ancient species, is that afforded by the large ex- 

 ternal bones which form the head and large bony dermal scales 

 upon the body of the modern Sturgeons, which further agree with 

 these fossils in having no internal bony skeleton. 



Another analogy occurs in the large external bones of the head 

 of the Flying Fish, and of the common Gurnard. These bones are 

 also beautifully studded with ornamental tubercles, arranged in 

 symmetrical groups like gems and pearls on a jewel. This cha- 

 racter is most strongly dominant in the tuberculated bones of the 

 fossil genus Coccosteus. The enormous proportion in the size of 

 the head to that of the body in the Gurnard, affords another ap- 

 proximation to a condition of frecpient occurrence in the extinct 

 genera of the old red sandstone, and which has given its character- 

 istic feature to the genus Cephalaspis. 



Another frequent character in the fossil fishes of the old red sand- 

 stone consists in the absence of any internal bony skeleton, as in the 

 modern Sturgeons. The large bony dermal scales, first noticed many 

 years ago in the old red sandstone of Fife by Dr. Fleming, and then 

 referred by him to a fossil Sturgeon, have been confirmed by Prof. 

 Agassiz as belonging to a genus nearly allied to the modern Stur- 

 geon, and like it possessed a cartilaginous skeleton, of which no 

 traces remain in the fossil state. 



Among living fishes, a further analogy to this cartilaginous 

 condition of the internal skeleton has recently been found by Pro- 

 fessor Owen in the Siren, a fish of equivocal aspect, provided with 

 lungs as well as branchiise, and considered as a reptile by preceding 

 writers ; it lives in the muddy bottoms of the shalloAv lakes of Se- 

 negal, which are periodically dried up, the fish meantime remaining 

 immured alive in a kind of cocoon of indurated mud*. In the car- 

 tilaginous skeleton of this existing Siren from Senegal, the anatomy 

 of which has been admirably demonstrated by Professor Owen, we 

 find a beautiful analogy to the cartilaginous condition of the skeleton 



* Sec Annals, vol. vi. p. 4G(); vii. \^. 28. 



