SUB-CLASS I 



SELACHII 



21 



Mesacantlius mitchdli. Eg. sp. Lower Old Red Sandstone ; Faniell, 

 Forfarshire. Nat. size (after Egerton). 



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

 spines. Cii'cumorbital 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 of Scotland. 31. 

 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 



Acanthodes xvardi, Eg. ,i -f-> • ,i ^ , l^ n ^ • c 



Skeletal parts of pectoral fln, smooth. Kaugiug throughout the Uarboniterous in 

 England!' ^"Honow'ba'ai Scotland, the Coal Measures in England and North 

 element ; r, Dermal rays ; s, America, and the Lower Permian in France, Germany, 



Dermal spme formmg an- .' -i c\•^ • a i -a i • -i 



terior border of ttn (after ijohemia, and Siberia. A. bronni, Ag., the typical 

 bmi oofwar ). species, about 0"3 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. 



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, triangular teeth. A. wardi, H. and A., from Coal 

 Measures of Xorthumberland and Midlothian. 



Acanthodes gracilis, Beyr. Scales from the outer (A, C) and 

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



