FOSSIL FISHES. 15 



anterior to the bony arches which strengthen the occipital portion, a de- 

 pressed area (as seen from the inner side), where some flat rad lately- stri- 

 ated bones are crushed up against the roof of the skull. Possibly the 

 brain was completely encased in bone, but the obscure and confused ap- 

 pearance of the under side of the cranium has led me to infer that a con- 

 siderable portion of the original structure was cartilage. 



Two detached cranial bones found with the head, by Mr. Terrell, and 

 referred to on another page, evidently correspond with those figured by 

 Hugh Miller and Pander, as belonging to the anterior part of the head of 

 Asterolepis, and partially inclosing the eye-orbits. 



A pair of large bones, not before met with, formed part of the great 

 skeleton of Bmiohthys, quarried out at ShefBeld last year, by Mr. Terrell. 

 They are nearly two feet in length, at one end somewhat fan-shaped, flat, 

 and about seven inches wide, at the other narrow and bifurcate. These 

 would be called Coraco-scapular bones by Gill, Coracoids by Owen and 

 Gunther, and Clavicles by Parker. They will be referred to again in the 

 notes on Dinichthys TerrelU. 



The fins of Dinichthys are only made known to us by a single frag- 

 ment, six inches long by three or four wide. This is apparently a por- 

 tion of a median fin, of which the rays are as thick as one's little finger, 

 and well ossified. Several large flat plates have been found associated 

 with the bones described above, but their places are not yet fully deter- 

 mined. They will be noticed more at length in the description of D. 

 TerrelU. 



From the foregoing remarks it will be seen that the discovery of Di- 

 nichthys is a matter of interest, not simply because it adds another and the 

 most gigantic to a strange, extinct group of fishes, but also because it 

 serves as a connecting link between several genera of Devonian Placo- 

 derms, of which the aflinities have been somewhat obscure, viz. : Goccos- 

 teus and Pterichthys with Asterolepis and MeterosUus ; and more especial- 

 ly because it shows a relationship to exist between these peculiar fishes and 

 the anomalous living Lepidosiren. 



The finding of a living species of Ceratodus (C. Forsteri) and its care- 

 ful study by Dr. Gunther, have apparently resulted in tracing a genetic 

 line from Dipterus of the Devonian, through Ctenodus of the Carbonif- 

 erous, and Ceratodus of the Trias, to one marked form of living Dipnoans. 

 From what we have seen of the resemblance in structure between Lepido- 

 siren and Dinichthys, we may conclude that a parallel Hue ran upward 

 from the Devonian Placoderms to the other living branch of the Dipnoan 

 family, now represented by Lepidosiren and Protopterus. The links in 

 this chain have not yet been found, but there is little doubt that they 

 win hereafter be discovered. 



