100 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



form, also fishes from a similar horizon at Wallyford, near Musselburgh, at Lochgelly in 

 Fifeshire, and at Possil in Lanarkshire. Unfortunately, the jaws and dentition have only 

 been verified in the specimens from the Borough Lee Ironstone. And here it may be as 

 well to place together the forms in outline of the maxillary bone in the three known 

 species of Gonatodus, to show how characteristic for each is the contour of that element. 



Fig. 3. — Contour of the maxillary bone in the three species of Gonatodus: a. O. punctaiui, h. O. macrolcpis, 



c. O. parvidens. 



In the maxilla figured on PI. XXI, the posterior margin of the bone is inclined 

 somewhat downwards and forwards, but this is rather exceptional, the margin in question 

 being, as in the above text- figure, normally nearly vertical. 



Geological Position and Localities. — A fish of the upper part of the Lower Carboni- 

 ferous series in Central Scotland. 



Edge Coal Series : Borough Lee Ironstone at Borough Lee and Loanhead, near 

 Edinburgh. Ironstone near Great Seam (?), Wallyford, near Musselburgh. Lower 

 Possil Ironstone, Possil, Lanarkshire. Ironstone in Edge Coal Series, Lochgelly, 

 Fifeshire. 



Lower Limestone Series : In the roof shale of the " South Parrot " coal seam, 

 Niddrie, near Edinburgh. 



Genus — Diiydenius, Traquair, 1800. 



Gonatodus (pars), Traquair. 



Generic Characters. — Form of body fusiform ; pectoral fins not known, dorsal fin 

 nearly opposite the space between the ventrals and the anal ; dorsal and anal triangular- 

 acuminate, many rayed; caudal heterocercal and inequilobate; all the fins fulcrated ; 

 scales rhombic, ganoid ; maxilla and dentary of mandible, each with one row of small, 

 closely-set cylindro-conical teeth ; splenial with a similar row along its upper margin, and 

 also with a similar group of large curved teeth springing from its inner surface below 

 the upper margin. 



The salient generic character of Brydenius is the peculiar dental armature of the 

 splenial bone, otherwise the resemblance to Gonatodus is very close. 



