GANOIDEI. 



329 



cranial bones, and the teeth are conical in form and nearly 

 equal in size. The species of Dipterus are all Devonian. 



Fig. 289. Jaw of Rhizodus Hibberti. Carboniferous. 



The family Phanopleurini comprises only the single genus 

 Phaneroplenron (fig. 290), which is probably exclusively De- 

 vonian. In this singular genus the scales are very thin, 

 cycloidal, and overlapping one another. The dorsal fin is 

 extremely long, and is confluent with the tail-fin, and the pec- 

 torals and ventrals are acutely lobate. The jaws are armed 

 with a single series of short conical teeth, and the notochord 

 was persistent. 



Fig. 290. P haneropleuron A ndersoni and scale. Devonian. 



Lastly, the family of the Ccdacanthi comprises forms which 

 range from the Devonian to the Cretaceous period, and which 

 are distinguished, in the typical genera, by having hollow fin- 

 spines, by having two dorsal fins, each supported by a single 

 interspinous bone, by having cycloidal overlapping scales, and 

 by the remarkable peculiarity that the swim-bladder was ossi- 

 fied. The type-genus Calacanthus seems to range from the 

 Carboniferous to the Trias. 



