ORDERS OF FISHES. 



145 



The family Phanopleurini comprises only the single genus 

 Phaneropleuron (fig. 510), 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 

 pectorals and ventrals are acutely lobate. The jaws are 

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

 notochord was persistent. 



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Fig. 510. — Pkanaropleuron Aiulcrsoni and scale. Devonian. 



Lastly, the family of the Ccelacantliini 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 the possession of 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 ossified. The type-genus Cmlacanthus 

 seems to range from the Carboniferous to the Trias. 



SUB-OEDER E. AcANTHODiD^. — Scales exceedingly small, 

 shagreen-like ; the front of each fin provided with a strong 

 spine, simply implanted in the flesh ; no distinctly ossified 

 cranial bones ; no operculum ; tail heterocercal. In their 

 fin-spines, and in some other points, the Accmthodidm ap- 

 proximate closely to the ElasmohrancJiii ; but they are gener- 

 ally regarded as an order of the Ganoidei. The AcantJiodido3 

 are mainly Devonian, but some forms occur in the Carbon- 

 iferous rocks, and two species from the Permian rocks have 



VOL. II. K 



