SUB-CLASS V GANOIDEl , 75 



nally ornamented with striae, rugae, or reticulations. The remote dorsal and 



anal fins opposed to each other ; the diphycercal caudal fin truncated at its 



hinder margin. Of the four series of imbricating keeled 



dermal scutes one extends along the back, another along the 



ventral border, and the other two smaller series along the 



flanks. The ventral scutes form a ring round the region 



of the anus. Belouorhynchvs occurs in the Trias of the Alps ^.^^ ^3^ 



(Raibl, Perledo, Seefeld) and Australia (Hawkesbury Forma- smmchthys acumi- 



tion), and is represented by skulls and other fragments in nat*^'^size"°' lUiaetic' 



the Lias of England and G-ermany (Belonostomus acidus, Ag.). Kemnatii.wurtem- 



The teeth, jaws, and skulls from the Muschelkalk, Keuper, 



and Rhaetic, described under the name of Saurichthys, Ag. (Fig. 134), probably 



lielong to Belonorliynclms. 



Order 3. HBTEROCBRCI. Zittel.i 



Notocliord persistent, hut arches, spinous processes, and fin supports more or less 

 ossified ; head covered with bony dermal plates. Opercular apjjaratus well developed, 

 and branchiostegal rays numerous. Infraclavicle present. Unpaired, and usually 

 also paired fins fringed with fulcra. Paired fins without seedy axis, hut each pelvic 

 fin with a row of imperfectly ossified hasal supports. A single dorsal and anal fin, 

 with articulated rays which are more numerous than their supports. Caudal fin 

 heterocercal. Scales rhombic or rhomhoidal, rarely cycloidal. 



In their skeletal structure and the characters of their paired fins, the 

 Heterocerci agree so closely with the Chondrostei, that they are united with 

 the latter by Traquair under the ordinal name of Acipenseroidei. In their 

 outward aspect they bear a superficial resemblance to the Lepidostei. The 

 Chondrostei, Heterocerci, and Lepidostei, probably form three different 

 specialised branches from one and the same primitive group. 



Family 1. Palaeoniscidae. Vogt emend. Traquair. 



Trunk elongate-fusiform. Head bones more or less enamelled. Teeth slender, 

 conical or styliform. Scales ganoid, rhombic in shape, rarely cycloid on the trunk. 

 Devonian to Upper Jurassic. 



Cheirolepis, Ag. Jaws with an outer roAv of minute teeth and an inner row 

 of stouter teeth. Dorsal fin remote, arising behind the origin of the anal fin. 

 Scales very small, rhombic, or almost square. C. cummingiae, Ag. ; Lower Old 

 Eed Sandstone, Scotland. C. canadensis, Whiteaves. Upper Devonian ; Scau- 

 menac Bay, Canada. 



Canobius, Gonatodus, Traquair. Lower Carboniferous ; Scotland. G. moly- 

 neuxi, Traq. ; English Coal Measures. 



Amblypterus, Ag. Mouth and teeth small. Fins with delicate fulcra. 

 Scales smooth. Several species from Lower Permian (Rothliegendes) of 

 Rhenish Prussia, Bohemia, and France. A. latus, Ag. ; A. duvernoyi, Ag. sp. 



Eurylepis, Newb. (Fig. 135). Small fishes with small fins, the fin rays not 



^ Traquair, R. H., The Ganoid Fishes of the British Carboniferous Formations (Palaeont. Soc.) 

 No. 1, 1877, No. 2, 1901. — On Amhlypterus, Palaeoniscus, Gyrolepis, and Pygopterus (Quart. Journ. 

 Geol. Soc. vol. XXXIII.), 1877.— On Eskdale Fishes (Trans. Roy. Soc. Edinb. vol. XXX.), 1881. 



