192 



ACANTHODII 



Family Diplacanthidae. The spines are much developed, may be 

 serrated and grooved ; they usually occur between the pectoral and 

 pelvic tins. In Diplacanthus there are two pectoral spines on each side 

 (Fig. 163). There are two dorsal fins, and usually clavicular plates. 



Diplacanthus, Ag. (Fig. 156, A); Parexus, Ag. ; Mesacanthus (Fig. 

 164, B) ; Ischnacanthus, Eg. ; Devonian, Scotland. Glimatius, Ag. 

 (Fig. 164, A); Devonian, Scotland and England. 



Family Acanthodidae. The intermediate spines are vestigial or 

 absent ; the remaining spines are more slender ; there is only a single 



A CUmatius scutiger, Eg., Lower Old Bed Sandstone, Forfarshire ; B, Mesacanthus Mitchelli, 

 E» ibid ■ C Acanthodes mlcatus, Ag., Lower Carboniferous, Edinburgh ; D, Acanthodes tiracUi , 

 Ko'i'iner i.ower Permian, Bohemia ; restored outlines. (A after A. S. Woodward, B and C 

 after Traquair, 1> alter Fritsch, from A. S. Woodward, l'roc. Geol. Assoc.) a, anal, d, dorsal, 

 p, pectoral, and v, pelvic Bns; l.sp, paired ventral spines. 



dorsal fin ; and the pelvic fin tends to dwindle in size as the pectoral 

 becomes larger. 



Acanthodes (Acanthoessus), Ag. ; Devonian, Europe and N. America 

 (Fi". 164, C and D) ; Carboniferous and Permian, Europe. Cheir acanthus, 

 Ag? (Fig. 158); Devonian, Scotland. Acanthodopsis, H. and A.; Car- 

 boniferous, Great Britain. Protacanthodes, Fr. ; Permian, Europe. 



Incertae sedis. 



Family Gyracanthidae. Isolated large spines and small tubercles,. 



found in Palaeozoic deposits, and to which the names Gyracanthus and 



Oracanthus have been given, have long been a puzzle to palaeontologists. 



Quite recently, A. S. Woodward has shown that they belong to a fish 



