24 BRITISH FOSSILS. 



Fam. 4. — Ctenododipterini. -^^r 

 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. 



Fam. 6. — Ccelacanthtni. - ,1 



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

 scales cycloidal ; paired fins obtusely lobate ; air bladder 

 ossified. 



Ccelacanthus, Undi7ia, Macropoma. 

 SuBORDo IV. — Chondrosteid^. 



SUBORDO V. — ACANTHODIDiE. 



Considering the Ganoid ei, as defined by Miiller, to form an order 

 of the class Pisces, and adopting the four groups typified by Amia, 

 Lepidosteus, Accipensev and Acanthodes, respectively, as subor- 

 ders, without thereby prejudicing the question as to whether other 

 suborders may not be required, I propose to establish another and 

 equivalent group, or suborder, to comprise the existing Polypterus 

 and all those e:5itinct Ganoids which, like it, fall within the range 

 of the following definition : — 



Dorsal fins two, or, if single, multifid or very long ; the pectoral and 

 usually the ventral fins, lobate; no branchiostegal rays, but two principal, 

 with sometimes lateral and median, jugular plates, situated between the 

 rami of the mandible ; caudal fin diphycercal, or heterocercal ; scales 

 cycloid or rhomboid, smooth or sculptured. 



On the suborder thus defined I propose to confer the title of 

 CEOSSOPTERYGiDiE,* in consideration of the peculiar manner in which 

 the fin rays of the paired fins are arranged, so as to form a fringe 

 round a central lobe, which constitutes so marked a character of all 

 the genera belonging to the group at present known. 



The characters of five of the six families which compose this 

 suborder have been given, incidentally, in the preceding pages, but 

 the table contains another family wdiose collocation with the rest 

 requires justification. 



* Kpocra-uThs, irrepv^, "fringed tin." " Crossotopterygidaj " would perhaps be more 

 correct, but the shorter compound is preferable. 



