SUB-CLASS IV 



DIPNOI 



63 



within outwards. Two pairs of jugular plates. Paired fins acutely lobate, 

 the pelvic pair remote and opposed to the anterior of the two dorsal fins ; 

 anal fin opposite the posterior dorsal ; tail heterocercal. Trunk and fins 

 covered with thick, deeply overlapping scales, which are nearly rhombic in 

 their exposed portion and invested with punctate ganoine. Complete, but 

 mostly flattened and distorted examples of Dipterus are not uncommon in the 

 Lower Old Red Sandstone of Northern 

 Scotland. Dental plates very abundant 

 in Middle and Upper Devonian of central 

 and eastern United States. 



Scanmenacia, Traq. Upper Devonian ; 

 Canada. 



Phaneropleuron, Huxley (Fig. 117). 

 Upper dental plates triangular, with 

 straight and crenulated radiating ridges. 

 Long; dorsal fin continuous with the 

 caudal, but small anal fin separate. 

 Scales very thin and cycloid, marked 



P. ander- 

 known by well - preserved 

 specimens from Upper Old Red Sand- 

 stone, Fifeshire. 



Palaedaphus, van Beneden (Heliodus, 

 Xewb.), (Fig. 118). Only known by 

 mandible and detached dental plates. In ^SSffSS^!^&. 



P. insiqnis, van Ben. and de Koninck, each Newsham, Northumberland (after Hancock and 

 u , , , . r\ -i fr Atthey). Oral surface of teeth really concave. 



lower dental plate, measuring lrl7 m. 



in length, bears four smooth, obtuse radiating ridges. Upper Devonian ; 



Belgium and Pennsylvania. 



( 'dnchodus, M'Coy ; Synthetodus, Eastman. Devonian. 



Ctenodus, Ag. (Fig. 116). Hinder border of cranial roof with one median 

 occipital plate, with a pair of plates immediately adjoining in front. Dental 



with delicate radiating striae 

 soni, Huxl., 



Fig. 116. 



Pterygo-palatim 

 Coal Measures 



Fig. 117. 



Phaneroplewon andersoni, Huxley. Upper old Red Sandstone ; Dura Den, Fifeshire. 



V;; nat. size (after Page). 



plates with numerous tuberculated or crenulated radiating ridges. Dorsal 



