340 



THE WONDERS OF GEOLOGY. 



Lect. IV. 



in four orders, which are distinguished by the structure of 

 the scales, as exemplified in the following tables {Lign. 68). 



Order I. The Pktcoid ; the skin covered with irregular enamel- 

 led plates, as in the Rays, Sharks {Lign. 68, fig. 2). 

 II. The Ganoid ; the scales of an angular form, and com- 

 posed of plates of horn or bone covered with a thick 

 layer of enamel ; as in the Sturgeon (Lign. 68, fig. 1). 



III. The Ctenoid; the scales formed of plates, which are 

 toothed or pectinated on their posterior margin or 

 edge, like a comb ; as in the Perch (Lign. 68, fig. 4). 



IY. The Cycloid; the scales composed of simple laminae of 

 horn or bone, without enamel, and having smooth 

 borders ; as in the Salmon (Lign. 68, fig. 3).* 



2 3 



Lign. 69. — Scales of fishes in flint. 



Fig. 1. A fragment of flint containing two scales, of the natural size. 



2. One of the scales highly magnified; it belongs to the species of Beryx, 



figured in Lign. 68. 



3. The other scale highly magnified; it belongs to the species of Smelt, figured 



in Lign. 72, fig. 1. 



Patches of scales are very abundant in some of the white 

 chalk strata in Sussex and Kent ; and occasionally very 

 perfect examples of the entire body of the fish, with the fins 

 attached, are obtained ; which by proper dissection may be 



* See Medals of Creation, vol. ii. p. 593. 



