768 



MR. E. S. GOODRICH ON 



[Nov. 12, 



Devonian genera, Phaneropleuron and Scavmienacia (PI. XLIY. 

 figs. 10 & 11, and text-fig. 201). These fish have thin scales, with- 

 out cosmine or ganoine, but studded all over with the same 

 characteristic spines. This Dipnoan type of scale would seem to 

 be a degenerate form derived from the cosmoid type of Dipterus^ 

 after the loss of the cosmine layer. We may expect to find inter- 

 mediate scales among the other extinct Dipnoi. 



The Ganoid Scales. — Ganoid scales, whether of the palteoniscoid 

 or of the lepidosteoid type, are found only in the Actinopteiygii 

 (and Polypterini). 



^ All the Palfeoniscidse and Platysomidse I have been able to 

 examine, have scales belonging to the Palseoniscoid type, differing 



Text-fig. 202. 



(From Lankester's ' Treatise on Zoology,' by permission of Messrs. A. & C. Black.) 



CJieirolepis sp., L. Devonian. A. Transverse section of scale. B. Outer view of 

 scales enlarged. C. Much enlarged view of a piece of a scale cut transversely. 

 D. A fragment of the inner bony layer, magnified, dt., canaliculi of cosmine 

 layer; /., vertical blind canals (pulp-cavities) ; g., ganoine layer ; Ji., system of 

 horizontal vascular canals ; i., inner bony layer, isopedine ; s., shiny outer 

 surface ; vc, vertical canal. 



only in unimportant details {Palceoniscus elegans ; Eurynotus 

 crenatus, text-fig. 198 ; Elonichthys, Gonatodus, PL XLY. fig. 15). 

 They can be recognised at once in sections by the presence of a 

 network of canals and a layer of cosmine underlying the laminae 

 of ganoine. 



The scale of Cheirolepis, the structure of which is shown in 

 PI. XLY. fig. 13 and text-fig. 202, has all these characters well 

 developed in spite of its small size and peculiar shape. 



