GANOIDEI. . 327 



Fam. 4. CTENODIPTERINI. 



Dorsal fins two ; scales cycloidal ; pectorals and ventrals acutely 

 lobate ; dentition ctenodont. 



Dipterus [Ceratodus? Tristichopterus ?] 



Fam. 5. PHANEROPLEURINI. 



Dorsal fin single, very long, not subdivided, supported by many 

 interspinous bones ; scales thin, cycloidal ; teeth conical ; ven- 

 tral fins very long, acutely lobate. 



Phaneropleuron (fig. 290). 

 Fam. 6. CCELACANTHINI. 



Dorsal fins two, each supported by a single interspinous bone ; 

 scales cycloidal ; paired fins obtusely lobate ; air-bladder ossi- 

 fied. Calacanthus, Undina, Macropoma. 



As regards the distribution of the Crossopterygida in time, 

 Professor Huxley remarks: " Of the six families which com- 

 pose it, four are not only Palaeozoic, but are, some exclusively, 

 and all chiefly, confined to rocks of Devonian age an epoch 

 in which, so far as our present knowledge goes, no fish belong- 

 ing to the sub-orders of the Amiadce and Lepidosteida (un- 

 less Cheirolepis be one of the latter) makes its appearance. 

 Rapidly diminishing in number, the Crossopterygidae seem to 

 have had several representatives in the Carboniferous epoch ; 

 but after this period (unless Ceratodus be a Ctenodipterine) 

 they are continued through the Mesozoic age only by a thin, 

 though continuous, line of Ccelacanthini, and terminate, at the 

 present day, in the two or three known species of the single 

 genus Polypterus" 



Of the extinct types of this sub-order, some are sufficiently 

 important to merit especial mention. In the family of the 

 Saurodipterini, the genus Osteolcpis (fig. 282) has a very hetero- 

 cercal tail and smooth scales. The first dorsal is placed near 

 the centre of the back, and the mouth is furnished with sharp 

 teeth. All the species of this genus are Devonian. The Car- 

 boniferous genus Megalichthys appears also to belong here. 

 In this singular genus are large " sauroid " fishes with hetero- 

 cercal tails, rhomboidal scales, and great conical incurved teeth, 

 which are mostly smooth, but are sometimes finely ridged. 



Of the Glyptodipterini with rhomboidal scales, Glyptolcemus 

 (fig. 287) may be taken as the type. In this singular fish, the 

 body is elongated and the head depressed. There are two 

 dorsal fins which are placed very far back, and the ventrals 

 have a similar posterior position. The tail is " divided into 

 two equal lobes by the prolonged conical termination of the 

 body," becoming thus " diphycercal." Glyptolamus is exclu- 

 sively confined to the Devonian period. 



