758 



MR. E. S. GOODRICH ON 



[Nov. 12, 



Text-fig. 198. 

 o. 



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



'Euri/Hotus crenatus Ag. ; Lower Carboniferous. A. Diagrammatic and much 

 enlarged view of a piece of the scale. B. Enlarged outer view of a scale. 

 C. Transverse section of a scale, enlarged. «., anterior covered region ; ap., 

 articulating process; c, fine canaliculi of cosmine layer; g., ganoine layer; 

 7i., system of horizontal canals ; i., isopedine layer; o., opening on outer surface 

 of vertical canals ; p., posterior exposed shiny surface ; s., outer surface ; 

 vc, vertical canal. 



During growth the three kinds of tissue are laid down simul- 

 taneously and in continuity ; but the articulating peg and the 

 flange which is overlapped by the neighbouring scales are formed 

 of bone only. 



The Lepidosteoid Sccde. — While resembling the Palaeoniscoid 

 scale in its general appearance and mode of growth, the scale of 

 Lepidosteus differs from it in two important pai-ticulars (text- 

 figs. 199 & 200). In the first place there is no horizontal network of 

 vascular canals giving off canaliculi — there is therefore no regular 

 zone of cosmine. In the second place, the scale is pierced by a 

 multitude of slender unbranched tubules passing inwards from the 

 surface at right angles to the lines of growth (PI. XL VI. fig. 20). 

 These tubules converge therefore towards the central or oldest 

 region of the scale, and many of them penetrate to quite near the 

 ganoine. As has been well shown by IIertwig(7) and ISTickerson (13), 

 each tubule belongs to one cell, which lies on the surface of the 

 scale and sends a long process down the tubule. At their inner 

 extremities the tubules break up into minute branching twigs. 

 In some cases, as for instance in Lepidotus, these fine branches 

 pass upwards at the edges with some regulaiit}^, where the bony 

 lamellse merge into the ganoine. Williamson speaks of this region 



