SUB-CLASS I 



SELACHII 



21 



Fig. 36. 



Mesacanthus mifchelli, Eg. sp. Lower Old Red Sandstone ; Farnell, 

 Forfarshire. Nat. size (after Egerton). 



Mesacanthus, Traquair (Fig. 36). A gracefully fusiform fish with slender 



spines. Circumorbital ring of four plates. Pelvic fins not much smaller than 



the pectorals, about mid- 



way between these and 



the anal ; a pair of minute 



spines between the paired 



fins. Dorsal fin more or 



less opposed to the anal, 



but not in advance of it. 



Mesacanthus mitchelli, 



Egert. sp. (Fig. 36); 31. 



peachi, Egert. sp. ; and 



M. pusillus, Ag. sp., from 



the Lower Old Eed Sand- 

 stone of Scotland. M. 



affinis, Whiteaves sp., an equally small species from the Upper Devonian of 

 Scaumenac Bay, Province of Quebec, Canada. 



Acanthodes, Ag. (Acanthoessus, Ag. ; Holacanthodes, 

 Beyr. ; Traquairia, Fritsch), (Figs. 37, 38). A more 

 elongated fish with similarly remote dorsal fin, but 

 the pelvic fins relatively small and advanced forwards, 

 the pectorals larger, and intermediate spines absent. 

 Teeth minute or absent ; circumorbital ring of four 

 more or less sculptured plates. Pectoral fin spine 

 supported by a hollow, mesially constricted element 

 (Fig. 37, b), which abuts against the side of its proximal 

 end ; a close series of short, fine dermal rays (r ) some- 

 times appearing below this in the fin membrane. Scales 

 smooth. Ranging throughout the Carboniferous in 

 Scotland, the Goal Measures in England and North 

 America, and the Lower Permian in France, Germany, 

 Bohemia, and Siberia. A. bronni, Ag., the typical 

 species, about 0*3 m. in length, from the Rothliegende 



of Rhenish Prussia (Lebach and Saarbrücken). A. gmcilis, Beyr. (Fig. 38), 



from Klein Neundorf, Silesia, 



probably identical with the 



latter. A. wardi, Egert., from 



Goal Measures, Longton, 



Staff'ordshire. 



Cheiracanthus, Ag. Like 



Acanthodes, but dorsal fin arising 



in advance of anal, and scales 



sculptured. C. murchisoni, Ag., 



and other species from Lower 



Old Red Sandstone, Scotland. 

 Acanthodopsis, Hancock and 



Atthey. Jaws with few large, 



laterally compressed, triangulär teeth. A. wardi 



Measures of Northumberland and Midlothian. 



Acanthodes wardi, Eg. 

 Skeletal parts of pectoral fin, 

 nat. size. Goal Measnres ; 

 England, h, Hollow basal 

 element ; r, Dermal rays ; s, 

 Dermal spine forming an- 

 terior border of ün (after 

 .Smith Woodward). 



Fig. 38. 



Acanthodes gradlis, Beyr. Scales from the outer {A, C) and 

 inner (J5) aspects, much enlarged. Lower Permian ; Germany. j 



H. and A., from Goal 



