972 



CLASS PISCES. 



which an immature individual is shown in fig. 907, the dorsals are 

 placed immediately over the pelvic and anal fins. Both genera occur 

 in the Devonian of Scotland and Russia. Closely allied is the genus 

 Diplopterus, from the Scottish Carboniferous, in which the dorsal 

 fins are also situated posteriorly, the first being directly over the 

 pelvic. Megalichthys, from the same deposits, comprises two species 

 of large size ; and is characterised by the presence of large fulcra 

 at the roots of the pectoral, pelvic, and anal fins ; and also by the 



Fig. 907. — A young individual of Thursius macro lepido tus ; from the Devonian of Scotland. 

 Letters as in fig. 900. Reduced. (After Sedgwick and Murchison.) 



small size of the anterior dorsal fin, which is placed above the 

 pelvic fin. Ectosteorhachis, from the Permian of North America, 

 is nearly related, and appears to be the last survivor of the family. 

 The second subfamily, or GlyptolcemituB, is represented only by the 

 genera Glyptolcemus (fig. 908) and Glyptopomus, of the Scottish 

 Devonian ; and differs from the last by the sculptured scales, and 

 the absence of a middle jugular plate. The body is much elon- 

 gated ; there is a long interval between the pectoral and the posterior 



-Glyptolcemus Kinnairdi; from the Devonian of Scotland. 

 (After Huxley.) 



Reduced, a. Scales. 



fins ; and the tail is truly diphycercal ; each genus is represented 

 by a single species. 



Family Ccelacanthid^e. — With this family we come upon a 

 group of fishes not occurring in the older Palaeozoic, but extending 

 from the Carboniferous to the Upper Cretaceous, and thus affording 

 a link between the preceding extinct and the following existing 

 family. The vertebral column is unossified ; there are two dorsal 

 fins, each of which is supported by a single forked interspinous 

 bone j the pectoral fins are obtusely lobate \ the caudal fin is un- 



