SUB-CLASS I 



SELACHII 



21 



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); M. 

 peachi, Egert. sp. ; and 

 M. pusillus, Ag. sp., from 

 the Lower Old Red Sand- 

 stone 

 affinis, 



Fit 



at). 



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

 Forfarshire. Nat. size (after Egerton). 



of Scotland. M. 



\Yhiteaves sp., an equally small species from the Upper Devonian of 

 Scaumenac Bay, Province of Quebec, Canada. 



Acanthodes, Ag. (Acanthoessus, Ag. ; Holacanthod> ?s, 

 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 Coal Measures in England and North 

 America, and the Lower Permian in France, Germany, 

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

 species, about 03 m. in length, from the Rothliegende 



of Rhenish Prussia (Lebach and Saarbriicken). A. gracilis, Beyr. (Fig. 38), 



from Klein Neundorf, Silesia, 



probably identical with the 



latter. A. wardi, Egert., from 



Coal Measures, Longton, 



Staffordshire. 



Cheir acanthus, 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, triangular teeth. A. 



Measures of Northumberland and Midlothian 



Acanthodes wardi, Eg. 



Skeletal parts of pectoral fin, 

 nat. size. Coal Measures ; 

 England, b, Hollow basal 

 element ; r, Dermal rays ; s, 

 Dermal spine forming an- 

 terior border of fin (after 

 Smith Woodward). 



/; 



Fig. 3S. 



Acanthodes gracilis, Beyr. Scales from the outer (.!,') and 

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



wardi, EL and A., from Coal 



