142 ORDERS OF FISHES. 



Sub-fam. — Saurodipterini (Osteolepis, Diplop- 

 terus, Megalichthijs), 



b. Scales cycloiclal, sculptured. 



Fam. 4. — Cyclodipteridse {Tristichopterus, Gyro- 

 ptychiiis (?), Bhizodus, Ehizodo2)sis, Strepsodus, 

 Arddchthys (?) ). 



C. Pectorals acutely lobate, scales cycloidal. 



a. Dorsal fins two, veutrals sub-acutely lobate, scales 

 thick, sculptured. 



Fam. 5. — Holoptychiidse {Holoptychius, Glyptolepis, 

 Dendrodus (?), Cricodus (?) ). 



h. Dorsal fin elongated, continuous with the upper part 



of the caudal ; ventral fins acutely lobate ; scales thin. 



Fam. 6. — Phaneropleuridae {Phaneroplem'on, Uro- 



nemus). 



As regards the distribution of the Crossopterygidm in time, 

 I'rofessor Huxley remarks : " Of the six families which 

 compose it, four are not only Pala3ozoic, but are, some ex- 

 clusively, and all chiefly, confined to rocks of Devonian age 

 — an epoch in which, so far as our present knowledge goes, 

 no fish belonging to the sub -orders of the Amiadce and 

 Lepiclostcidm (unless Chcirolc^ns be one of the latter) makes 

 its appearance. Eapidly diminishing in number, the Crosso- 

 pterygidse seem to have had several representatives in the 

 Carboniferous epoch ; but after this period (unless Ceratodus 

 be a Ctcnodipterine) they are continued through the Mesozoic 

 age only by a thin, though continuous, line of Coelacanthini, 

 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. 500) has a very 

 heterocercal tail and smooth scales. The first dorsal is 

 placed near the centre of the back, and the mouth is fur- 

 nished with sharp teeth. All the species of this genus are 

 Devonian. The Carboniferous genus Megcdichthys appears 

 also to belong here. In this singular genus are large " sau- 

 roid " fishes with heterocercal tails, rhomboidal scales, and 

 great conical incurved teeth, which are mostly smooth, but 

 are sometimes finely ridged. 



